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The Messenger
No. 179 – Quarter 1 | 2020
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SPHERE Unveils the True Face of the Largest Main Belt Asteroids
2018 Visiting Committee Report
The ASPECS Survey
ESO, the European Southern Observa- Contents
tory, is the foremost intergovernmental
astronomy organisation in Europe. It is The Organisation
supported by 16 Member States: Austria, Rix H.-W. – The 2018 Visiting Committee Report 3
Belgium, the Czech Republic, Denmark, Barcons X. – Following Up on the Recommendations of the Visiting Committee 5
France, Finland, Germany, Ireland, Italy,
the Netherlands, Poland, Portugal, Spain, Telescopes and Instrumentation
Sweden, Switzerland and the United Schmidtobreick L. et al. – NaCo — The Story of a Lifetime 7
Kingdom, along with the host country of
Chile and with Australia as a Strategic Astronomical Science
Partner. ESO’s programme is focused Vernazza P. et al. – SPHERE Unveils the True Face of the
on the design, construction and opera- Largest Main Belt Asteroids 13
tion of powerful ground-based observing Aravena M. et al. – The ASPECS Survey: An ALMA Large Programme
facilities. ESO operates three observato- Targeting the Hubble Ultra-Deep Field 17
ries in Chile: at La Silla, at P
aranal, site of Pietrzyński G. et al. – The Araucaria Project Establishes the
the Very Large Telescope, and at Llano Most Precise Benchmark for Cosmic Distances 24
de Chajnantor. ESO is the European
partner in the Atacama Large Millimeter/ Astronomical News
submillimeter Array (ALMA). Currently Patat F. et al. – ESO’s Peer Review Panel Achieves Gender Balance 30
ESO is engaged in the construction of the Saviane I. et al. – Report on the ESO Workshop
Extremely Large Telescope. “The Galactic Bulge at the Crossroads” 31
Saviane I. et al. – Report on the ESO Workshop “The La Silla Observatory —
The Messenger is published, in hardcopy From Inauguration to the Future” 36
and electronic form, four times a year. Belfiore F., Thomas R., Navarrete C. – Fellows at ESO 41
ESO produces and distributes a wide Personnel Movements 44
variety of media connected to its activi-
ties. For further information, including Annual Index 2019 (Nos. 175–178) 46
postal subscription to The Messenger,
contact the ESO Department of Commu-
nication at:
ESO Headquarters
Karl-Schwarzschild-Straße 2
85748 Garching bei München, Germany
Phone +498932006-0
information@eso.org
The Messenger
Editor: Gaitee A. J. Hussain
Layout, Typesetting, Graphics:
Lorenzo Benassi, Jutta Boxheimer
Design, P roduction: Jutta Boxheimer
Proofreading: Peter Grimley
w ww.eso.org/messenger/
Printed by omb2 Print GmbH,
Lindberghstraße 17, 80939 Munich,
Germany
Unless otherwise indicated, all images in
The Messenger are courtesy of ESO,
except authored contributions which are
Front cover: The unique capabilities of the SPHERE instrument on
courtesy of the respective authors. ESO’s Very Large Telescope have enabled it to obtain the sharpest
images of a double asteroid as it flew by Earth on 25 May 2019.
© ESO 2020 While this double asteroid was not itself a threatening object, sci-
ISSN 0722-6691 entists used the opportunity to rehearse the response to a hazard-
ous Near-Earth Object (NEO), proving that ESO’s front-line tech-
nology could play a key role in planetary defence. This artist’s
impression shows both components of the double asteroid 1999
KW4 during its Earth fly-by. Credit: ESO/M. Kornmesser
2 The Messenger 179 – Quarter 1 | 2020
The Organisation DOI: 10.18727/0722-6691/5184
The 2018 Visiting Committee Report
Hans-Walter Rix 1 and history. Looking to the future, the VC challenges are successfully met.
concluded that ESO is indeed set for ESO is aware of those challenges, and
a successful implementation of the ELT if some of them have been emphasised
1
MPIA, Heidelberg, Germany the Organisation — and its Council — in the VC’s recommendations.
address a number of challenges, some of
which are pointed out in this report. ESO should continue to optimise its
ESO’s activities are externally assessed organisational health and efficiency by:
every few years by a Visiting Committee strengthening both strategic planning
composed of a panel of senior external ESO’s strengths and excellence of, and agility in, personnel recruitment
experts who report their findings to the and fostering in-house mobility; amelio-
ESO Council and Director General. The The VC found ESO to be a world-class rating both overbooking and project-
assessment is based on an extensive science organisation, truly exceptional in multiplexing among individual staff mem-
set of presentations, reports and inter- many respects. It has implemented and bers; ensuring that long-term planning
views with ESO staff conducted during is operating a suite of observatories and security for ELT key expertise remains
visits to all ESO sites. Here we summa- instrumentation that is unrivalled in its feasible within the matrix framework; and
rise the report and recommendations combination of quality and breadth; the continuing to improve the communica-
produced as a result of the latest Visit- success of the Very Large Telescope tion flow, both upwards and downwards,
ing Committee assessment, which took Interferometer (VLTI) with the adaptive- within the Organisation.
place at the end of 2018 and was pre- optics-assisted, two-object, multiple
sented to the ESO Council in June 2019. beam-combiner GRAVITY is just one
example. ESO’s facilities enable its user ELT implementation
community to carry out astrophysics on a
The ESO Visiting Committee (VC) offers par with other world-class facilities. The The VC was very impressed with the
its external assessment of how ESO is VC notes that Atacama Large Millimeter/ state of the ELT planning and implemen-
complying with its mission to provide submillimeter Array (ALMA) astrophysics tation, as well as ESO’s awareness of
world-class facilities for astronomy and to carried out by the ESO community is truly the complexity and enormity of this ambi-
foster astronomical collaborations. To outstanding at a global level. tious project. In light of the complexity,
this end, the VC considered the competi- the VC recommends that ESO pay even
tiveness of the research carried out by The basic organisational structure within closer attention to two aspects. First, a
the ESO community and evaluated the ESO is suited to its tasks, and it has tightly integrated telescope-instrumentation-
calibre and range of ESO’s observatory a track record of adapting to new chal- operations approach is key to the timely
activities. The VC also looked at ESO’s lenges. ESO can also draw on a deep success of the ELT and an important
organisational health and readiness to pool of talent; the VC found a high level of aspect of mitigating budgetary and
reach its strategic goals, in particular the staff dedication to its mission, and gener- scheduling risks; these three aspects of
implementation of the Extremely Large ally high employee motivation with a posi- the ELT must be tied together even more
Telescope (ELT) programme. tive gradient. closely than in the case of the Very Large
Telescope (VLT). Second, strong and
This report is based on the VC’s two site The VC found that, in looking towards coherent scientific leadership of the over-
visits — carried out between 22 and the future, ESO leadership appears to all ELT effort must be in place throughout
26 October and 19 and 27 November be striking a good balance between its implementation.
2018 in Garching and Chile, respectively ambitious vision, dedication to excellence
— and extensive materials provided in its observatory facilities and moving The VC also considered other aspects
before and during these site visits. The towards healthy planning realism. of ESO, such as its outreach strategy
report was informed by numerous direct and the involvement in the Atacama
interactions with ESO staff at all levels Pathfinder EXperiment (APEX) and the
of the Organisation. All of the main rec- Optimising ESO’s organisational Cherenkov Telescope Array (CTA).
ommendations reported here reflect con- structure
sensus within the VC.
In light of these strengths, the VC paid Summary of recommendations
The VC came to the conclusion that, particular attention to the question of
at present, not only is ESO fulfilling the whether ESO is ready to implement the Articulating the current ESO strategy
essential elements of its mission ELT in the coming decade while continu-
superbly, but it is also a beacon of sci- ing to maintain its cutting-edge strengths ESO has successfully implemented most
ence in Europe and the world and a at the existing observatories (i.e., the of the strategic vision that was laid out
global leader in astronomy. Internally, La Silla Paranal Observatory) and sus- in 2004. The VC recommends that the
ESO is a strong and largely healthy taining its strong role in ALMA. It is the ESO Council and the Director General
organisation, with strains and issues VC’s view that ESO can accomplish this, develop and formally document ESO’s
at a level that is to be expected for an as there are no obvious show-stoppers, strategic vision for the next decade. The
endeavour of this ambition, complexity and that it will succeed if a number of VC strongly supports ESO’s overriding
The Messenger 179 – Quarter 1 | 2020 3
The Organisation Rix H.-W., The 2018 Visiting Committee Report
focus on the implementation of the ELT experienced by some staff; and finding On CTA implementation
while maintaining current strengths. The ways to assure long-term planning
VC therefore acknowledges and supports security for key ELT expertise within the The VC concurs with ESO that CTA is an
the conclusion that any responsible articu matrix framework. exciting scientific prospect in collabora-
lation of the current strategy may leave lit- tion with a strong consortium. The VC is
tle or no room for the implementation of also concerned that unforeseen efforts
any other major new programmes in the Strategic and efficient recruitment related to CTA on ESO’s part could dis-
near future. tract from the implementation of the ELT
Among aspects of organisational effi- and strongly recommends that ESO’s pri-
ciency, extensive near-term recruitment oritisation, role and effort in CTA do not
Ensuring the budget envelope for ESO’s of highly qualified personnel will be key grow beyond what is currently planned.
mission to ESO’s mission success in the coming
years. The VC recommends that ESO
The VC appreciates ESO’s current rigour review all aspects and all actors involved On the future of APEX
and realism in determining the resources in efficiently and successfully bringing in
needed for the implementation of the new talent; this is to ensure that recruit- APEX is currently working well and pro-
ELT. It is the VC’s view that, as an organi- ment is both proactive and strategic, as ducing good science. The VC recom-
sation, ESO is robust and efficient well as efficient and rapid in practice. The mends that ESO examine critically
enough to successfully implement the VC also recommends that ESO continue whether APEX will remain scientifically
ELT within the currently forecast resource to improve the effectiveness of in-house indispensable for its user community
need, which strains the contribution career mobility and development. as ALMA matures, beyond the current
envelope of the Member States. The VC contractual arrangement.
strongly encourages the ESO Council
to push for the provision of the required A close telescope-instrumentation-
(forecast) budget, as this will indeed operations approach for the ELT On education and outreach strategy
ensure ESO’s global leadership in astron-
omy for decades to come. In light of the ELT’s complexity, the VC The VC recommends that ESO clarify
recommends that ESO pay close atten- and strengthen its vision, and implemen-
tion to a very tightly integrated telescope- tation, of its education and outreach
Optimising ESO’s organisational health instrumentation-operations approach. effort, with a closer integration and coor-
and efficiency In the VC’s view, this is key to the timely dination of these activities in Europe
success of the ELT and is an important and Chile. In Garching, the VC sees a
The VC found ESO to be a strong, healthy aspect of mitigating budgetary and serious risk that the tremendous potential
and efficient organisation overall, with scheduling risks. Specifically, the VC of ESO’s Supernova will not be realised,
highly talented and motivated staff. recommends that the ELT Programme given its current lean level of staffing.
The organisational strains that will inevita- deepen its connections with both the The VC was unconvinced that augment-
bly result from ESO’s ambitious plans external instrument teams and the future ing the current operations model merely
will require continued and strengthened LPO operations team, in a spirit of close by external fundraising alone would lead
effort towards organisational optimisation. collaboration. to an education and outreach effort that
lives up to ESO’s vision.
Specific recommendations follow:
– The VC recommends that ESO con- Overall science leadership for the ELT
tinue to address or mitigate both Note
the historic and the inevitable political The VC recommends that ESO ensure a
The Visiting Committee 2018 was composed of
differences in its staff arrangements, strong science leadership of the overall Masimo Altarelli, Rebecca Bernstein (Vice-Chair),
such as aspects of the 50/50–80/20 ELT effort as it will be critical to the ELT’s Sofia Feltzing, Robert Kennicutt, Anne-Marie
science/duty contracts for scientists, or long-term scientific success and impact. Lagrange, Hilton Lewis, Elena Pian, Hans-Walter
aspects of the international/local staff Such leadership is key to fully considering Rix (Chair) and Patrick Roche.
categories among technical and scien- the needs of the telescope, the instru-
tific staff in Chile. ments, the AO and the operations from
– The optimisation of the matrix structure the viewpoint of the ELT’s overall scientific
at ESO Garching, which has gained utility; it will also ensure that appropriate
widespread acceptance, must c ontinue trade-offs are made between performance
by: eliminating or reducing oversub- and capability on the one hand, and
scription of staff resources; addressing budget, schedule and risk on the other.
the extensive project fragmentation
4 The Messenger 179 – Quarter 1 | 2020
The Organisation DOI: 10.18727/0722-6691/5185
Following Up on the Recommendations of
the Visiting Committee
Xavier Barcons 1 The ultimate goal of this exercise is to risks and costs of building the ELT and
obtain external and expert guidance bringing it into operation; continuing to
on areas where action needs to be taken, recruit the necessary staff to support
1
ESO at the very least because there is always the ELT — avoiding overloading and pro-
room for improvement. However, as a ject fragmentation in the matrix; intensify-
member of ESO, it is also rewarding to ing the understanding between ELT
Like most scientific organisations, ESO read in the report that in the committee’s construction and Paranal operations as
periodically invites advice from an view ESO is fulfilling its mission very well as enhancing ESO’s technical
external expert panel that assesses the well, and that with the support of Council involvement in ELT instrument develop-
performance of the Organisation, and the adoption of a number of recom- ment; empowering and further support-
and formulates a number of recommen- mendations the Organisation is bound to ing the ELT Programme Scientist in over-
dations. The most recent ESO Visiting succeed in its current endeavour, that seeing all scientific aspects of the ELT;
Committee travelled to all of the ESO of building and bringing into operation clarifying the interfaces with CTA-South
sites in the last months of 2018 and the ELT, while maintaining the VLT/I and to ensure that the project develops
delivered its report to Council in June ALMA at the forefront of worldwide without affecting the other projects in
2019. The committee, whose composi- astronomy. It gave me great pleasure to Paranal; discussing the future of the
tion and mandate had been approved convey the congratulations of the Visiting Atacama Pathfinder EXperiment (APEX)
by ESO Council, was constituted by Committee to all ESO personnel. in a cost-neutral way for ESO and defin-
a set of internationally renowned scien- ing a communication strategy that capi-
tists who possess complementary A number of actions aligned with the Vis- talises on ESO’s scientific achievements
areas of expertise covering all aspects iting Committee recommendations are and the added value of ESO’s pro-
of ESO’s function. I am extremely grate- now being taken after discussion with the grammes to society.
ful to all committee members for their ESO Council. Updates on these actions
hard work and very careful preparation will be reported to and discussed with I have no doubt that the recommenda-
of their report. An extract of the main Council as they progress. The ongoing tions of the Visiting Committee will
conclusions and recommendations is actions include: support to ESO Council strengthen ESO and increase the likeli-
presented in the preceding article. in discussing an updated strategy; a hood that it succeeds in its mission.
careful and continuous updating of the
ESO/B. Tafreshi (twanight.org)
Paranal Observatory
with the Milky Way
appearing to stretch
directly upwards
from one of the Unit
Telescopes.
The Messenger 179 – Quarter 1 | 2020 5
Telescopes and Instrumentation
Enrico Sacchetti/ESO
Inside Antu (Unit Telescope 1) of the VLT. FORS2
(the yellow instrument) is mounted at the
Cassegrain and NaCo — seen here on the right —
is mounted at the Nasmyth B focus, with KMOS on
the left at the Nasmyth A focus.
Telescopes and Instrumentation DOI: 10.18727/0722-6691/5186
NaCo — The Story of a Lifetime
Linda Schmidtobreick 1 stellar clusters, Solar System objects, The odyssey begins
Nancy Ageorges 2 SN 1987A and several extragalactic
Paola Amico1 sources. We present a short history of Numerous boxes containing the many
Wolfgang Brandner 3 the life and achievements of NaCo from parts of NAOS and CONICA arrived at
Suzana Cerda 1 the viewpoint of the Instrument Opera- ESO’s Paranal Observatory on 24 Octo-
Claudia Cid 1 tion Team, Instrument Scientists, and ber 2001. Astronomers and engineers
Laird Close 4 Instrument Engineers. from ESO and the participating institutes
Eduardo Garces 1 and organisations a, b began the pains-
Gordon Gillet 5 taking task of assembly on the Nasmyth
Julien H. Girard 6 Introduction B platform of UT4 (see Figure 1). After
Patricia Guajardo 1 days of technical tests and adjustments,
George Hau 7 The Nasmyth Adaptive Optics System working around the clock, the team finally
Wolfgang Hummel 1 (NAOS) was developed by a French con- declared the instrument fit to attempt its
Yves Jung 1 sortium a in collaboration with ESO, and the first-light observation.
Markus Kasper 1 COudé Near-Infrared CAmera (CONICA)
Christopher Lidman 8 was built by a German consortium b in The UT4 dome was opened at sunset on
Lars Kristian Lundin 1 collaboration with ESO. Together they 25 November 2001 and a small, rather
Pedro Mardones 9 form NAOS-CONICA (NaCo) which was apprehensive, group gathered in the VLT
Dimitri Mawet 10 the first instrument with an adaptive Control Room, peering intensively at the
Jared O’Neal 11 optics (AO) system on the Very Large computer screens over the shoulders of
Emanuela Pompei 1 Telescope (VLT). It was first installed at their colleagues the telescope and instru-
Ricardo Schmutzer 1 the Nasmyth B focus of UT4 (Yepun), ment operators. As the basic calibrations
Karleyne Silva 12 where it stayed from 2001 through 2013. required at this early stage were success-
Jonathan Smoker 1 In 2014 it was reinstalled on UT1 (Antu) fully completed, the suspense rose, as
Christian Soenke 1 at the Nasmyth A. Early tests and results did expectations as the special moment
Lowell E. Tacconi-Garman 1 from commissioning runs showed that, approached when finally the telescope
Elena Valenti 1 by compensating for a large fraction operator pushed the button that sent the
Javier Valenzuela 1 of the atmospheric turbulence, it could telescope towards the first test object,
Jose Velasquez 1 obtain spatial resolutions close to the an otherwise undistinguished star in our
Gerard Zins 1 8-metre telescope’s diffraction limit. The Milky Way.
AO system was equipped with both visi-
ble and infrared, Shack–Hartmann type, The uncorrected image was recorded by
1
ESO wavefront sensors; the latter enabled the near-infrared imager and spectro-
2
KT Optics GmbH, Germany observations inside regions that are graph CONICA and it soon appeared on
3
MPIA, Heidelberg, Germany highly obscured by interstellar dust and
4
University of Arizona, Tucson, USA therefore unobservable in visible light.
Figure 1. NAOS (light blue) and CONICA (red) are
5
Independent engineer, Antofagasta, For almost 18 years, NaCo provided multi- attached to the Nasmyth B adapter of UT4 (Yepun).
Chile mode, AO-corrected observations in the The control electronics are housed in the white
6
STSCI, Baltimore, USA 1–5 μm range. c abinets.
7
University of Bath, UK
8
Australian National University,
Canberra, Australia
9
Universidad de Valparaiso, Chile
10
Caltech/JPL, Pasadena, USA
11
Argonne National Laboratory,
Lemont, USA
12
Gemini Observatory, La Serena, Chile
NaCo was switched off on 2 October
2019, almost 18 years after its first light.
The last exposure was of the standard
star HD590 as part of the close-out
calibrations. To date, 699 papers have
been published using NaCo data,
including observations of the Galactic
centre, direct images of exoplanets
orbiting their stars, young stellar
objects, brown dwarfs, massive stars,
The Messenger 179 – Quarter 1 | 2020 7
Telescopes and Instrumentation Schmidtobreick L. et al., NaCo — The Story of a Lifetime
the computer screen. With a full width Figure 2 (left). The first image with
NAOS-CONICA of a star (V magnitude
half maximum (FWHM) diameter of only
of 8) obtained before (left) and
0.50 arcseconds, it already showed good after (right) the adaptive optics was
image quality, thanks to the atmospheric switched on.
conditions on that night. Then the NAOS Uncorrected AO corrected
image image
adaptive optics system was switched
FWHM: 0.50″ FWHM: 0.07″
on, thereby “closing the loop” for the first
time on a celestial object. As the deform-
able mirror in NAOS began to follow
the “orders” that were being issued 400
times a second by its control computer, Figure 3 (below). The giant planet
the stellar image on the computer screen S aturn as observed with the VLT
NAOS-CONICA Adaptive Optics
seemed to pull itself together. What sec- Left: uncorrected Right: corrected
instrument on 8 December 2001.
onds before had been a jumping, blurry
patch of light suddenly became a rock-
steady, razor-sharp and brilliant spot. The
entire room burst into applause with
happy faces and smiles all round. Nowa-
days, we are used to getting these sharp
and steady images whenever the loop
of an adaptive optics system closes. But
at the time of NaCo’s first light, this must
have been a truly magical moment. The
diameter of this first image was measured
as 0.068 arcseconds (see Figure 2).
Even during those early tests and com-
missioning nights, NaCo delivered
impressive astronomical results. Among
the first images to be obtained was one
of the stellar cluster NGC 3603, a high
mass star-forming region. Only with the
new, high-resolution K-band images was
it possible to finally study the elusive
ESO/S. Gillessen et al.
class of brown dwarfs in such a starburst
environment. Another early highlight
was the observation of Io, the innermost
of the four Galilean moons of Jupiter
and the most volcanically active place in
the Solar System (see press release
eso0204 1 for details). And then of course,
there was the “Lord of the Rings”, Saturn
itself, in all its beauty. These observations
were very challenging. CONICA’s field of
view had to be steadied on Saturn, NAOS
had to track the small moon Tethys, the
reference source for the adaptive optics,
and UT4 was tracking a star used for
Figure 4. The central parts of our
determining active optics corrections g alaxy as observed in the near-
and autoguiding. As Figure 3 shows, it infrared with NaCo. By following the
worked. motions of the most central stars over
more than 16 years, astronomers were
able to determine the mass of the
However, the commissioning itself was supermassive black hole in the centre.
also under a lot of pressure. Firstly, there
was strong competition for precious con- and NaCo was supposed to start moni- and it became a key instrument for moni-
sole places because the fibre positioner toring this region. There was a big rush to toring the motions of the stars close to
for FLAMES was being commissioned at get NaCo operational in time for an early the Galactic centre for many years. By
the same time. Secondly, the centre of epoch observation. In fact, NaCo turned measuring these stellar orbits with such
our Galaxy becomes observable in April out to perform excellently (see Figure 4) amazing precision, it was possible to
8 The Messenger 179 – Quarter 1 | 2020
conclude that the central invisible object Figure 5. This composite image shows
an exoplanet (the red spot on the
is very likely to be a supermassive black
lower left), orbiting the brown dwarf
hole (Gillessen et al., 2009). 2M1207 (centre). 2M1207b is the
first exoplanet directly imaged and the
first discovered orbiting a brown
dwarf. It was imaged for the first time
The early years
with NaCo on UT4 in 2004.
Not everything worked immediately
though and that’s why NaCo is also a
story of encounters and friendships
between astronomers, amazing engi-
neers and dedicated telescope opera-
tors. From the beginning, the instrument
appeared to have its own moods and
people had to comply with these to
successfully operate NaCo and keep it
observing through the night. Sometimes
it just didn’t work, often it required enor-
mous effort and c ollaboration between
various departments to get it up and
running. Only with time and improved
monitoring were these moods attributed but also very nervously as it was not clear prism which allowed simultaneous spec-
— at least to a large degree — to specific whether Paranal was in the right viewing troscopy from J- to M-band, the installa-
atmospheric behaviour. In this way, NaCo zone. When the event did happen, the tion of order-sorting filters that allowed
also taught us the importance of monitor- tension broke and the visiting astronomer L-band and H+K-band spectroscopy at
ing and recording ambient physical prop- started applauding and kissed his wife. various spectral resolutions, and the
erties as well as instrumental perfor- Afterwards everyone involved celebrated Fabry-Perot interferometer to take narrow-
mance, now regular practice with all with excellent French cheese the smell of band observations tunable between
instruments. which lingered until the next day. 2 and 2.5 µm. Also the detector was
upgraded, the new Aladdin III detector
Then there have been all the unforeseen Another of these special moments was having better cosmetics, linear range and
circumstances: when the only NaCo- the observation of 2M1207, a brown readout noise.
trained night astronomer fell sick just dwarf in the young TW Hya association.
before the first visiting observer run, and In a series of NaCo exposures, a tiny red However, the NaCo instrument concept
a colleague had to take over at the last speck of light was discovered only was always considered a flexible one,
minute; when, in the aftermath of NASA’s 0.8 arcseconds away from 2M1207 (see and this triggered new ideas about how
Deep Impact mission 2, NaCo broke Figure 5). The thrill of seeing this faint to extend and optimise the capabilities
down just before the time-critical obser- source of light in real-time on the instru- of NaCo, especially for certain astronomi
vations, was urgently fixed and was still ment display is indescribable. Was this cal applications. For example, exoplanets,
cooling down at the most crucial moment; actually a planet orbiting the brown where for any kind of direct imaging
and when the NAOS field selector broke, dwarf? A spectrum taken with NaCo the main problem is the high contrast
requiring two intensive weeks on the shows the signatures of water molecules between the light of the host star and the
mountain to repair it. The Instrument Sci- and confirms that the object must be light of the planet. Of course, larger plan-
entist at the time also vividly remembers comparatively small, cold and of about ets are easier to observe, as are planets
the time when UT4 was observing with five Jupiter masses. However, to prove around faint stars. It is no surprise that
the Spectrograph for INtegral Field Obser- that it is a planet orbiting the brown dwarf, the first imaged planet was a giant, Jupiter-
vations in the Near Infrared (SINFONI) more images over a longer time interval like planet around a brown dwarf. To
under wonderful conditions and they had to be obtained. Only a year later, it decrease the contrast between star and
needed to check some NAOS connec- was c onfirmed that indeed NaCo had planet, new modes were invented, such
tion. They opened one of the cabinets taken the first image of a planet outside as simultaneous differential imaging
and caused a complete shutdown of the our Solar System (Chauvin et al., 2005). (Lenzen et al., 2004), the four-quadrant
telescope — and a shock for everyone phase mask together with a Lyot-Stop
involved. coronograph (Boccaletti et al., 2004),
New observing modes a pupil stabilised mode for Angular Differ-
On the other hand, there have been ential Imaging (Kasper et al., 2009), the
numerous special moments, like the Pluto After several years of operation, a num- Apodising-Phase-Plate coronograph
occultation, when astronomers, opera- ber of previously planned upgrades to (Kenworthy et al., 2010), and the Annular-
tors, engineers and everyone else were NaCo were carried out (Kasper et al., Groove-Phase-Mask (AGPM) corono-
all waiting enthusiastically for the event, 2005). These included the low-resolution graph (Mawet et al., 2013). NaCo served
The Messenger 179 – Quarter 1 | 2020 9
Telescopes and Instrumentation Schmidtobreick L. et al., NaCo — The Story of a Lifetime
as a testbed to implement and evaluate Dear outstanding professionals,
all of them.
two nights ago our NACO had the last whisper on sky after observing a bright star.
Other attempts were made to increase
the spatial resolution and get down to It’s been more than 20 years of amazing science and unique achievements!!
the diffraction limit with a well calibrated
point spread function. The interferometric Together we’ve seen things you people wouldn’t believe.
mode using Sparse Aperture Masking Engineers fighting their way through dichroics and wave front sensor. Astronomers
(SAM; Lacour et al., 2011) as well as worshipping a closed loop with seeing 2.0ʺ and coherence time 0.5 ms.
speckle holography (Schödel & Girard, We watched violent storms on Jupiter’s pole, planets orbiting desolate stars,
2012) and speckle imaging without AO Galactic Center glittering in the dark.
(Rengaswamy et al., 2014) served in All those moments will be lost in time, like tears in rain.
this respect and broadened the possibili- Time to die.
ties for NaCo science cases.
Your sincerely,
One of the major changes on Paranal in Antu on behalf of NACO
general but especially for NaCo and
SINFONI was the installation of the first ~~~~~~~~~~~~~~~~~~~~~~~~~~~
Laser Guide Star (LGS) facility, a collabo-
ration between ESO and MPE. NaCo had Estimados colegas,
to be upgraded for the extended spot
of the LGS. A System for Tip-tilt Removal dos noches atras NACO dio su ultima mirada al cielo.
with Avalanche Photodiodes (STRAP)
was installed, along with a new laser Fueron mas de 20 años de maravillosa ciencia y resultados unicos!!
dichroic and a new wavefront sensor len-
slet array with a larger field of view. The Juntos vimos cosas que ustedes no se pueden ni imaginar.
NaCo upgrade for LGSF was a collabora- Ingenieros enfrentandose con dicroicos y sensores de frente de onda.
tion between the Institut de Planétologie Astronomos cerrando el loop en condiciones proibitivas.
et d’Astrophysique de Grenoble (IPAG) Hemos visto tempestas al polo norte de Jupiter, planetas orbitando estrellas
and ESO, led by Gerard Zins who was at desoladas, el Centro Galactico parpadeando en la oscuridad.
IPAG at that time (Kasper et al., 2010). Todos estos momentos se perderan en el tiempo, como lagrimas en la lluvia.
Again, the collaboration made all the dif- Es tiempo de morir.
ference and much fun was had working
with the Garching AO group installing the Cariños,
laser. Even the non-AO astronomers viv- Antu por NACO
idly remember being involved in the first
nights of laser observations. Because the Figure 6. This email was sent by the support astron- needed to get everything up and running.
omers after NaCo’s last night of operation. It shows
automated plane detection software had NaCo’s facilities were drastically reduced
what NaCo means for most of us: lots of emotions,
not yet been approved for safety, every- lots of memories, and wonderful people working — no more spectroscopy and everything
body was helping out with plane spotting, together. had to be done in service mode, since
standing outside with a radio on the tele- Paranal did not have sufficient engineer-
scope platform, watching the sky, and close to the black hole that the extreme ing resources to keep all the modes up
sending the stop-propagation order if a gravity would make the effects of general and running.
plane was getting too close. relativity detectable. For this event, new
instruments like GRAVITY were created, Apart from the regular Galactic centre
but an instrument was needed to actually observations, another main science
The final years follow the star and determine the precise driver was the imaging of planets with the
orbit before and after the encounter. new AGPM mask, and the reduced NaCo
In 2013, NaCo was supposed to be So, in 2014 NaCo was brought back to was of course also offered in open time
decommissioned. However, an important life, this time installed on the Nasmyth A to the community. In 2018, after a major
astronomical event was on the horizon — focus of UT1. Consternation arose when problem with the detector controler, the
the close encounter of the star S2 with it became clear that the CONICA detec- visible wavefront sensor had to be
the black hole in the centre of our Galaxy. tor couldn’t be brought back to life. Luck- decommissioned. At that time, NaCo
As mentioned above, since the beginning ily, ISAAC had been decommissioned required several hours attention to be
of its operation NaCo played a key role a few years before and had also been operational at night and may have become
in monitoring the motions of stars close equipped with an Aladdin detector. So the most cursed instrument on Paranal
to our Galactic centre. Now in 2018, the old ISAAC detector was refurbished but, when working, it delivered spectacu-
one of these stars, S2, which has a highly and put into NaCo. Some long and lar images; the monitoring and astrometry
elliptical orbit, was supposed to get so frustrating re-commissioning runs were of the Galactic centre was a great success
10 The Messenger 179 – Quarter 1 | 2020(GRAVITY Collaboration et al., 2018) and Explorer (MUSE) and the Enhanced Kenworthy, M. et al. 2010, The Messenger, 141, 2
Lacour, S. et al. 2011, The Messenger, 146, 18
even in its old age NaCo was still contrib- Resolution Imager and Spectrograph
Lenzen, R. et al. 2004, SPIE, 5492, 970
uting to exciting science results. At the (ERIS) are being operated at Paranal or Mawet, D. et al. 2013, A&A, 552, L13
moment of writing, 699 papers have been will be coming soon. AO techniques will Rengaswamy, S. et al. 2014, The Messenger, 155, 12
published using NaCo data 3. be key for any instrument on the ELT in Schödel, R. & Girard, J. H. 2012, The Messenger,
150, 26
future. All of these operational modes
NaCo’s last night of operation, 1 October were originally tested on NaCo. We are
2019, was cloudy, so a planned last-light continuously improving these techniques Links
image of Io could not be taken. Last light but, to quote a former Instrument Scien-
1
SO Press Release 0204 showing NaCo image of
E
was instead recorded from the standard tist, “NaCo was instrumental in making
Saturn’s rings: http://www.eso.org/public/news/
star HD590 at 04:22:50 UT on 30 Sep- adaptive optics mainstream”. eso0204
tember 2019. After that last night of oper- 2
N ASA Deep Impact mission: https://www.jpl.nasa.
ation, a very emotional email was sent gov/missions/deep-impact/
3
Acknowledgements Publications with NaCo: http://telbib.eso.org/?-
by the night crew to all colleagues in
boolany=or&boolaut=or&boolti=or&year-
Paranal (see Figure 6), expressing the We acknowledge the extensive use of ESO press to=2020&instrument%5B%5D=naco&boolins=or&-
emotions that we all felt when NaCo was releases, ESO newsletters and ESO images. Many booltel=or&search=Search
finally switched off. people have contributed to making NaCo observa-
4
NaCo’s history: www.eso.org/sci/facilities/paranal/
tions possible. We would like to thank the engineers decommissioned/naco/History.html
and scientists who built the instrument, and those
who developed and installed new modes at later
Beyond NaCo stages, the various commissioning teams, the hard- Notes
ware and software engineers who kept this delicate
a
instrument in good shape, the colleagues in he French consortium consisted of Office National
T
NaCo leaves a legacy of amazing data
Garching working on instrumental upgrades, pipe- d’Etudes et de Recherches Aérospatiales (ONERA),
that are available in the archive. The pipe- line development, quality control and user support, Laboratoire d’Astrophysique de Grenoble (LAOG)
line will be kept alive and updated with all the members of the Instrument Operation Team and Observatoire de Paris (DESPA and DASGAL).
system changes in order to ensure the over the time, and all the support astronomers and The Project Manager was Gérard Rousset
telescope operators using NaCo at UT1 or UT4. Last (ONERA), the Instrument Responsible was François
ongoing use of these data. A history of
but not least, we would like to thank the astronomi- Lacombe (Observatoire de Paris) and the Project
NaCo, in particular a list of events that cal community for their interest and for using NaCo Scientist was Anne-Marie Lagrange (Laboratoire
might influence which calibrations to take to advance their fascinating science cases. d’Astrophysique de Grenoble). It was supported by
for which epoch of observations is availa- the Institut National des Sciences de l’Univers
(INSU) of the Centre National de la Recherche Sci-
ble on NaCo’s webpage 4.
References entifique (CNRS).
b
T he German Consortium included the Max-Planck-
Of course, NaCo is not the end by any Boccaletti, A. et al. 2004, PASP, 116, 1061 Institut für Astronomie (MPIA) (Heidelberg) and the
means. AO continues to evolve, new Chauvin, G. et al. 2005, A&A, 438, L25 Max-Planck-Institut für Extraterrestrische Physik
Gillessen, S. et al. 2009, ApJ, 692, 1075 (MPE) (Garching). The Principal Investigator (PI) was
generations of AO instruments like the
GRAVITY Collaboration et al. 2018, A&A, 615, L15 Rainer Lenzen (MPIA), with Reiner Hofmann (MPE)
Spectro-Polarimetric High-contrast Kasper, M. et al. 2005, The Messenger, 119, 9 as Co-Investigator.
Exoplanet REsearch instrument Kasper, M. et al. 2009, The Messenger, 137, 8
(SPHERE), the Multi Unit Spectroscopic Kasper, M. et al. 2010, The Messenger, 140, 8
ESO/Callingham et al.
The VISIR instrument on ESO’s VLT captured this
stunning image of a newly-discovered massive
binary star system. Nicknamed Apep after an
ancient Egyptian deity, it could be the first gam-
ma-ray burst progenitor to be found in our galaxy.
The triple star system was captured by the
NACOadaptive optics instrument on the VLT.
The Messenger 179 – Quarter 1 | 2020 11Astronomical Science
ESO/M. Kornmesser
This artist’s impression shows the exiled asteroid
2004 EW95, the first carbon-rich asteroid con-
firmed to exist in the Kuiper Belt and a relic of the
primordial Solar System. This curious object likely
formed in the asteroid belt between Mars and
Jupiter and must have been transported billions of
kilometres from its origin to its current home in the
Kuiper Belt.Astronomical Science DOI: 10.18727/0722-6691/5187
SPHERE Unveils the True Face of the
Largest Main Belt Asteroids
Pierre Vernazza 1 Mars and Jupiter (typically between Explorer [OSIRIS-Rex], Hayabusa 1 & 2)
Laurent Jorda 1 2 and 3.3 astronomical units [au]). The or from remote imaging with the Hubble
Benoit Carry 2 diversity in their surface composition (for Space Telescope (HST) and adaptive-
Josef Hanuš 3 example, metallic iron, basalt, mixtures of optics-equipped ground-based tele-
Michaël Marsset 4 silicates such as olivine and pyroxene, scopes (for example, the VLT and the
Matti Viikinkoski 5 water-rich silicates, water ice) — as Keck Observatory) in the case of the larg-
Franck Marchis 1, 6 inferred from spectroscopic observations est bodies.
Miroslav Brož 3 — and their orbital distribution across the
Alexis Drouard 1 main belt (see, for example, Vernazza & The drastic increase in angular resolution
Thierry Fusco 1, 7 Beck, 2017 for a review) have provided (by about a factor of three) with respect
Romain Fétick1, 7 unique constraints to Solar System for- to the HST that is possible with the
Marin Ferrais 1 mation models which could not have new generation of adaptive optics using
& the HARISSA team been derived from observations of the the Zurich imaging polarimeter (ZIMPOL)
giant or telluric planets themselves. on SPHERE indicates that the largest
main-belt asteroids become resolvable
1
ix Marseille Université, CNRS, LAM
A It is now understood that the present- worlds and are thus no longer extended
(Laboratoire d’Astrophysique de day asteroid belt hosts bodies that were point sources. To place this in context,
Marseille), France formed at large heliocentric distances these asteroids have diameters greater
2
Université Côte d’Azur, Observatoire de (> 10 au) as well as bodies that may have than 100 km and angular sizes typically
la Côte d’Azur, CNRS, Laboratoire formed close to the Sun (< 1.5 au) and greater than 100 milliarcseconds (mas).
Lagrange, Nice, France that they have ended up at their current With the SPHERE instrument, craters
3
Institute of Astronomy, Charles Univer- location following giant planet migration with diameters greater than approxi-
sity, Prague, Czech Republic (see, for example, the Nice and Grand mately 30 km can now be identified on
4
Department of Earth, Atmospheric and Tack models; Levison et al., 2009; Walsh the surfaces of main-belt asteroids and
Planetary Sciences, MIT, Cambridge, et al., 2011) as well as gravitational inter- the shapes of the largest asteroids can
USA action with the embryos of the telluric be accurately reconstructed (for example,
5
Department of Mathematics and planets (Bottke et al., 2006). Broadly Marsset et al., 2017).
Statistics, Tampere University, Finland speaking, the idea that the asteroid belt
6
SETI Institute, Carl Sagan Center, is a condensed sample of the primordial To maximise the science return of the
Mountain View, USA Solar System has gradually emerged. SPHERE instrument in the field of aster-
7
ONERA/DOTA, Université Paris Saclay, oid studies, we proposed an ESO Large
Chatillon, France Whereas our understanding of the sur- Programme with the aim of characteris-
face composition of asteroids and its dis- ing the shape, density, internal and com-
tribution across the asteroid belt has positional structure, and surface topo
Over the past 2.5 years, we have been improved enormously over the last dec- graphy of a statistically significant fraction
carrying out disc-resolved observations ade, see recent reviews by Burbine (2014) of D > 100-kilometre main-belt asteroids
of a substantial fraction of all large and Vernazza & Beck (2017) the same (~ 35 out of ~ 200 asteroids). Our sample
(D > 100 km) main-belt asteroids, moni- cannot be said regarding their internal covers the major compositional classes
toring them at high angular resolution structure, which is best characterised (S, B/C, Ch/Cgh, X, P/D; DeMeo et al.,
throughout their rotation, and sampling by their density. To constrain the density, 2009; DeMeo & Carry, 2013). The survey
the main compositional classes, using one needs to fully reconstruct the 3D started in April 2017 and ended success-
the Spectro-Polarimetric High-contrast shape of a body, to estimate its volume fully in September 2019.
Exoplanet REsearch (SPHERE) instru- and to determine its mass from its
ment on the VLT. These observations gravitational interaction with other aster-
enable us to characterise the internal oids, preferably (whenever possible) with Methods
structure of our targets from their its own satellite(s).
density as well as their cratering record To achieve our science objectives, we
down to ~ 30 km in diameter. Such This is due to the fact that disc-resolved image our targets with SPHERE/ZIMPOL
information, in turn, places unpre observations of asteroids — contrary throughout their rotation (we collect
cedented constraints on models of the to disc-integrated observations of these images every ~ 60 degrees in planeto-
formation of the Solar System and same bodies (from light curves and/or centric longitude). These images are sub-
the collisional evolution of the main belt. visible and infrared spectroscopy) — sequently reduced and deconvolved
have so far been obtained with sufficient with the MISTRAL algorithm (Fusco et al.,
spatial resolution for only a few bodies, 2003; Mugnier, Conan & Fusco, 2004)
Scientific context either from dedicated interplanetary mis- using a point spread function (PSF).
sions (for example, Galileo, Near Earth At the beginning of our observing pro-
Asteroids are minor planets ranging in Asteroid Rendezvous (NEAR), Rosetta, gramme, we were observing a stellar PSF
size from a few metres to a few hundred Dawn, Origins-Spectral Interpretation- either before or just after every asteroid
kilometres which are located between Resource Identification-Security-Regolith observation. However, because the
The Messenger 179 – Quarter 1 | 2020 13Astronomical Science Vernazza P. et al., SPHERE Unveils the True Face of the Largest Main Belt Asteroids
deconvolution with the stellar PSF did not
produce systematically satisfactory Phase: 0.00 (2018-05-20T06:41:53:277)
results, we investigated alternative meth-
Lepida (~ 45 km)
ods to increase the sharpness of the
image. We noticed that in several cases Oppia (~ 40 km)
we achieved a better result by using
stellar PSFs acquired on different nights. Numisia (~ 30 km)
We therefore tested the deconvolution Urbinia (~ 24 km)
process with synthetic PSFs modeled by
Vestalia
a 2D Moffat function. The deconvolution Terra
using a Moffat PSF always converged
towards an acceptable solution by vary- Rheasilvia
ing the Moffat parameters (Fétick et al.,
2019). We therefore started systematically Eusebia (~ 26 km)
using a parametric PSF to deconvolve
our images (for example, Viikinkoski et al.,
Phase: 0.13 (2018-06-08T05:27:05:809)
2018; Fétick et al., 2019). Notably, the
case of Vesta (Figure 1) has confirmed the
accuracy of our image deconvolution
algorithm. Nevertheless, it is clear that Numisia (~ 30 km)
our programme provides a strong motiva-
Vestalia
tion for further development of deconvo- Terra
lution algorithms in order to limit artefacts
with additional priors, incorporate non-
axisymmetric features of the stellar PSF,
and improve convergence and stability.
Aricia tholus
The deconvolved images serve as input
to a 3D shape reconstruction algorithm
(ADAM; Viikinkoski, Kaasalainen & Durech,
2015 or MPCD; Jorda et al., 2016). Even Phase: 0.24 (2018-07-10T01:59:52:994)
though we already have low-resolution,
convex, shape models from existing
light curves for all our targets, the
SPHERE data allow us to drastically Aricia tholus
improve those models by producing more
realistic non-convex shape models, reveal- Octavia (~ 30 km)
ing the topography of individual craters
(D ≥ 30 km). Thus, thanks to SPHERE’s
unique angular resolution, we have been
able to open an entirely new window on
asteroid exploration. Cratering records that
are now available for our targets allow us to
address their global geology, as in the case
of (7) Iris for instance (Hanus et al., 2019). Hereafter, we summarise some of the Figure 1. Comparison of the VLT/SPHERE decon-
volved images of Vesta (left column) with synthetic
main results obtained so far. These
projections of the Dawn model produced with
The methods we employ to derive the results illustrate well the diversity of the OASIS and with albedo information (right column).
physical properties of our targets science questions that can be investi- The main structures that can be identified in both
have been validated in the case of the gated via such an imaging survey. the SPHERE images and the synthetic ones are
highlighted: craters are outlined by squares and
asteroid (21) Lutetia (Carry et al., 2010,
albedo features by circles. Reproduced from Fétick
2012), which is a relatively small object et al., 2019.
(D ~ 98 km) compared to our targets. A bluffing view of (4) Vesta
The asteroid was visited by the ESA tral properties similar to those of Vesta
Rosetta mission in 2010 (Sierks et al., With a mean diameter of 525 km (Russell (Binzel & Xu, 1993). It was understood
2011). With our methods, the inferred spin et al., 2013), (4) Vesta is the second larg- that these bodies originated as fragments
coordinates were accurate to one degree est body in the asteroid belt. In the early from Vesta that had been excavated in
and the absolute dimensions to within 1990s, telescopic observations of small one or more giant impacts. A few years
2 km with respect to those derived from asteroids on similar orbits revealed the later, observations performed with the
the Rosetta fly-by data. presence of numerous bodies with spec- HST revealed the presence of an impact
14 The Messenger 179 – Quarter 1 | 2020crater 460 km in diameter near the south
2017-07-10T09:06:56 2017-08-24T02:57:48
pole of Vesta (Thomas et al., 1997), thus
confirming the collisional origin of the
Vesta-like bodies. Later on, the NASA
Dawn mission characterised the surface
topography of Vesta in detail, revealing
the existence of two overlapping basins
in the south polar region and a central
peak whose height rivals that of Olympus
Mons on Mars (for example, Russell et
al., 2012; Jaumann et al., 2012; Marchi et
al., 2012; Schenk et al., 2012).
Nonza
Our SPHERE images have recovered the (D ~ 75 km)
surface of Vesta in great detail (Figure 1;
Fétick et al., 2019). Most of the main top- Figure 2. SPHERE/ZIMPOL images of (89) Julia oid population and because they enable
deconvolved with the MISTRAL algorithm. Nonza,
ographic features present across Vesta’s investigations of properties and pro-
the likely impact crater at the origin of a small colli-
surface can be readily recognised from sional family, is highlighted. cesses that are often difficult to probe by
the ground. These include the south pole other means. In particular, Earth-based
impact basin and its prominent central observations of binaries and triples pro-
peak, several D ≥ 25 kilometre-sized cra- studies, the future will only get brighter with vide the most powerful way of deriving
ters and also Matronalia Rupes, including the resolving power of the extremely large precise masses and thus densities for a
its steep scarp and its small and big arcs. telescopes (ESO’s ELT, the Thirty Meter substantial number of objects (for exam-
On the basis of our observations, it fol- Telescope [TMT], and the Giant Magellan ple, Descamps et al., 2011; Marchis et
lows that next-generation telescopes with Telescope [GMT]). All-sky surveys using al., 2013). The only other way to constrain
mirror sizes in the range 30–40 m (for the Vera C. Rubin Observatory will surely asteroid masses with similar precision
example, ESO’s ELT) should in principle discover many new small families. The is with dedicated interplanetary missions,
be able to resolve the remaining major follow-up with adaptive optics observa- either a fly-by for the largest ones (as in
topographic features of (4) Vesta (i.e., tions of their parent bodies may allow us to the case of (21) Lutetia) or a rendezvous
equatorial troughs, north-south crater reconstruct the respective impact craters (for example, the Dawn mission, OSIRIS-
dichotomy), provided that they operate at at the origin of these families. Rex and Hayabusa 1 & 2).
the diffraction limit in the visible.
At the same time, such investigations Direct imaging performed in the course
may help to establish new meteorite- of our Large Programme is a very effi-
A bright future for asteroid family asteroid connections. Indeed, asteroid cient way of discovering new moons,
studies families likely constitute a major source constraining their orbital parameters and
of meteorites. The case of Vesta supports hence the total mass of the system (pri-
Our SPHERE observations of asteroid such a hypothesis, it being likely that mary + secondary). In the case of a small
(89) Julia (Vernazza et al., 2018; Fig- the howardite-eucrite-diogenite (HED) secondary (which is always the case for
ure 2), a D ~ 140 km S-type asteroid and meteorites — achondrite meteorites our targets), the total mass is dominated
the parent body of a small collisional which account for about 6% of falls — by the primary, implying that the mass of
family that consists of 66 known mem- are derived from its family. In the near the primary can be well constrained (usu-
bers with D < 2.5 km, have revealed the future, it will therefore become possible ally with < 10% uncertainty).
presence of an impact crater (~ 75 km to search for the origin locations of
wide) that could be the origin of this fam- individual meteorite falls using their cos- Our programme has allowed us to dis-
ily. In addition, we studied both the mic ray exposure ages — which indicate cover a moon around the C-type asteroid
impact event by means of smoothed par- the time they have been traveling in (31) Euphrosyne (Vernazza et al., 2019).
ticular hydrodynamic simulations and space since being excavated from their With an estimated diameter of ~ 270 km,
the subsequent long-term orbital evolu- parent body — in conjunction with the Euphrosyne is so far the largest known
tion of the asteroid family, to determine its estimated asteroid family ages and main-belt asteroid with a companion.
age (30–120 Myr). It follows that the same high-angular-resolution imaging observa- We have also investigated the composi-
type of science investigation that could tions of the presumed parent bodies. tional structure of the binary asteroid (41)
be performed 20 years ago with the HST Daphne (Carry et al., 2019; Figure 3). Our
in the case of (4) Vesta and the discovery observations imply a density similar to
of its south pole impact basin at the Asteroids with satellites that of CM chondrites, and thus a homo-
origin of the Vesta family (Thomas et al., geneous internal structure for that object,
1997) can now be performed for many Multiple-asteroid systems (binaries, in agreement with numerical models sim-
D > 100 km main-belt asteroids with VLT/ triples) are important because they ulating the early thermal evolution of the
SPHERE. In the field of asteroid-family represent a sizable fraction of the aster- parent bodies of CM chondrites.
The Messenger 179 – Quarter 1 | 2020 15Astronomical Science Vernazza P. et al., SPHERE Unveils the True Face of the Largest Main Belt Asteroids
Figure 3. Images of (41) References
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Acknowledgements Vernazza, P. & Beck, P. 2017, Planetesimals: Early
and ground-based observations is get-
Differentiation and Consequences for Planets,
ting narrower (Fétick et al., 2019). With Pierre Vernazza, Benoit Carry, and Alexis Drouard (Cambridge, UK: Cambridge University Press),
the advent of extremely large telescopes were supported by CNRS/INSU/PNP. Josef Hanuš 269
(ESO’s ELT, GMT, TMT), the science was supported by the Czech Science Foundation Vernazza, P. et al. 2018, A&A, 618, A154
through grant 18-09470S. Thierry Fusco and Romain Vernazza, P. et al. 2019, CBET, 4627
objectives of future interplanetary mis-
Fétick are partially funded by DGA and ONERA. Viikinkoski, M., Kaasalainen, M. & Durech, J. 2015,
sions will have to be carefully thought out Michaël Marsset was supported by the National A&A, 576, A8
so that these missions will complement, Aeronautics and Space Administration under Grant Viikinkoski, M. et al. 2018, A&A, 619, L3
rather than duplicate, what will be No. 80NSSC18K0849 issued through the Planetary Walsh, K. J. et al. 2011, Nature, 475, 206
achieved via Earth-based telescopic Astronomy Program. Franck Marchis was supported
by NSF grant number 1743015.
observations. For instance, future ELT
ESO/M. Zamani
Paranal Observatory
at sunset.
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