La Silla Observatory of ESO in Chile
The La Silla Observatory is located on the outskirts of the Chilean Atacama Desert, 600 km north of Santiago de Chile and at an altitude of 2400 m. Like other observatories in this geographical area, La Silla is located far from sources of light pollution and, like the Paranal Observatory, home to the VLT (Very Large Telescope), it has one of the darkest night skies on the Earth. La Silla has been an ESO (European Southern Observatory) stronghold since the 1960s. Here, ESO operates two of the most productive 4 m class telescopes in the world. 1)
Figure 1: Photo of the La Silla Observatory, ESO's first observatory (image credit: ESO)
The 3.58 meter NTT (New Technology Telescope) broke new ground for telescope engineering and design and was the first in the world to have a computer-controlled main mirror (active optics), technology developed at ESO and now applied to most of the world's current large telescopes. The NTT is now home to the world's foremost extrasolar planet hunter: HARPS (High Accuracy Radial velocity Planet Searcher), a spectrograph with unrivalled precision.
The La Silla Observatory is the first world-class observatory to have been granted certification for the International Organization for Standardization (ISO) 9001 Quality Management System.
The La Silla geographical coordinates are: Latitude 29º 15' south & Longitude 70º 44' west.
Some background on the early history:
The idea of establishing a common large observatory that joined the European astronomers was born in the spring of 1953, in the mind of the renowned astronomer Walter Baade. This suggestion was then discussed, for the first time, by a group of astronomers at Leiden on June 21, 1953, after which they were invited to discuss it with their colleagues at home. Some months later, on January 26, 1954, twelve leading astronomers from six European countries: Belgium, France, Germany, Great Britain, the Netherlands and Sweden gathered in the Senate Room of Leiden University to discuss the idea of the recently suggested joint European observatory. Here, they issued a historical statement, which expressed the wish that the scientific organizations in their respective home countries recommended the establishment of a joint observatory in South Africa, equipped with a 3-m aperture telescope and a Schmidt telescope of 1.2 m aperture. The project was conceived to be completed over the next ten years and would need a convention between learned societies or between governments. In order to develop this project, an ESO Committee (EC) was formed. 2)
The ESO Convention: A first proposal for the convention between organizations was drafted in November 1954. Some of the most important features in that draft described the fact that financial contributions had to be proportional to the national income but only up to a fixed limit. Besides, the draft stated that the observatory should be located in the southern hemisphere and should have a large optical telescope and a Schmidt telescope as "Initial program", considering a future extension with any kind of other instrumentation. The southern hemisphere was the ideal choice, since most interesting objects of research could be reached from this hemisphere. In October 5, 1962, after years of meetings and struggles, the ESO Convention, between five of the first six countries was finally signed (Great Britain went its own way). The required ratification, however, was only completed in January 17, 1964, when parliamentary and financial commitments had been ensured. Hence, ESO was finally on solid grounds to begin its long-term building project.
Early in 1964, there was still a possibility of having a combined AURA-ESO settlement. Thus, in February 1964, in preparation for the final decision on the site for the ESO observatory, a group of 4 people was appointed in order to explore a variety of potential sites within the AURA domain, as well as in the general vicinity. Three mountains were inspected by helicopter and by car: Guatulame (southeast of Ovalle), Cinchado (a mountain within AURA territory) and Cinchado-North (outside the AURA domain). The latter turned out to be the most interesting one, from the point of view of accessibility, climate (dry), proximity of a flat area to be used for landing, and for being government property. Finally, on May 26, 1964, the final choice for ESO's site was the Cinchado-North mountain, also known as La Silla -name used at that time by the charcoal burners to refer to this mountain after its shape-. With this, the prospect of a combined AURA-ESO settlement was finally terminated. ESO Signs the Contract to Purchase La Silla.
In October 30, 1964 a contract was signed in Santiago between ESO and the Government of Chile, for the purchase of an area of 627 km2 including the mountain La Silla. The relatively low price paid by ESO, showed the interest on the part of the Chilean Government in having the observatory established in Chile.
The Growth of La Silla During 1964-1966: At the end of 1964, ESO had an office in La Serena functioning with five people, and had already a road project from Pelícano camp to the top of La Silla. The year 1965 saw much more progress, since apart from the road construction, Pelícano camp began to take its more definite shape. Similarly, a small temporary camp was constructed at La Silla, which included a storage room, some living quarters, a powerhouse and a temporary workshop. A year later, in 1966 a second, and more definite camp, was constructed near the top of La Silla. In January of that same year, the road connection to La Silla was completed; then, on March 24, 1966, the dedication of the road took place with the presence of many authorities and guests, such as the Archbishop of La Serena and the ESO’s President G. W. Funke.
The Inauguration: Three years after the dedication of the road, the first stage of the constructions had been finally completed, the middle-size telescopes had become operational while the hotel, the dormitories, a workshop, a storage space -among other facilities- had been completed as well. Thus, in March 25 1969, La Silla Observatory was inaugurated, with an audience of more than 300 people among Government officials, representatives of AURA and CARSO (Carnegie Southern Observatory, at las Campanas), besides staff members of ESO, and other guests. After two decades of growth, since the first initiatives towards La Silla creation in June 1953, the dream had become a reality.
La Silla Telescopes: In 1958 the EC appointed an Instrumentation Committee (IC), which should be in charge of the future instrumentation in La Silla. The IC was given two main tasks: preparing all technical and financial aspects of the instrumentation so as to enable the EC to take the necessary decisions, and making all necessary technical and instrumental decisions within the frame of the budget. Hence, one of the IC’s first assignments was the specification of the telescopes in La Silla; thus in 1961, they recommended the construction of the middle-size telescopes: 1 m and 1.5 m, both erected only in the second half of the 1960s. In 1968, the GPO (Grand Prism Objectif) was installed in La Silla to resume its work after eight years of service in the site testing activities in South Africa. In 1971, the 1.2 m Schmidt was finally installed in La Silla, as was the ESO 50 cm -a duplicate of the Copenhagen 50 cm. - Then, in November 1976, the largest telescope foreseen in the "initial program" the 3.6 m saw "first light". Subsequently, a 1.4m CAT (Coude Auxiliary Telescope) would feed a high-resolution spectrograph within the 3.6 m telescope building. In 1984, the 2.2 m began its operations, while in March 1989, the 3.5 m New Technology Telescope (NTT) saw "first light". Last, but not least, the SEST (Swedish ESO Submillimeter Telescope) is the only large submillimeter telescope (15 m diameter) in the southern hemisphere. It was built in 1987 on behalf of the Swedish Natural Science Research Council (NFR) and the European Southern Observatory.
National Telescopes: An extension of the telescope park not foreseen in the early days constituted the so-called National Telescopes. These are "telescopes which are property of one of the member states -or of an institute in one of these states- which are placed on La Silla and, as compensation for ESO services, ESO obtains a fraction of the observing time". The first telescope built under this category was the Bochum 61cm, installed in September 1968. The second one was the Danish 50 cm, called SAT (Strömgren Automatic Telescope) from the Copenhagen University Observatory in Denmark, whose operation began in 1971. A third one, the Danish 1.5 m, became operational in October 1979. The 90 cm Dutch Telescope –the "Light Collector", property of the Leiden Observatory in the Netherlands- was removed from its site at the Leiden Southern Station in South Africa, and re-erected at La Silla during 1978 and 1979. Lastly, ESO has granted full operational night to a number of projects run by their patronizing institutes. These are: Marly 1 m (Marseille Observatory), the Geneva 1.2 m (Geneva Observatory) and the DENIS (Côte d’Azur and Paris observatories).
Nowadays, only a few telescopes are under operation. The ESO 50 cm, Schmidt, CAT 1.4 m and Bochum 61 cm, have been decommissioned.
Figure 2: ESO operates observatories at three sites in Chile: Chajnantor (location of ALMA), Cerro Paranal (location of VLT) and Cerro La Silla (“Cerro” is the Spanish word for “Mountain”). In addition, ESO will construct the Extremely Large Telescope (ELT) at Cerro Armazones, near Paranal. This topographic map highlights the region in Chile in which the observatories are located and gives a magnified view of that area, showing the airports nearest to the sites and the connecting car routes, as well as the location of ESO offices (image credit: ESO)
The infrastructure of La Silla is also used by many of the ESO Member States for targeted projects such as the Swiss 1.2 m Leonhard Euler Telescope, the Rapid Eye Mount telescope (REM) and the TAROT Telescope gamma-ray burst chaser, as well as more common user facilities such as the MPG/ESO 2.2 m and the Danish 1.54 m Telescopes. The 67-million pixel Wide Field Imager on the MPG/ESO 2.2 m Telescope has taken many amazing images of celestial objects, some of which have now become icons in their own right.
Figure 3: La Silla Map and Safety (image credit: ESO)
Figure 4: An aerial view of the La Silla site in Chile, ESO's original observing site, located at the outskirts of the Chilean Atacama Desert, 600 km north of Santiago de Chile and at an altitude of 2400 m (image credit: ESO, C. Madsen)
Telescopes at La Silla
HARPS (High Accuracy Radial velocity Planet Searcher)
HARPS, the planet hunter, is the ESO facility for the measurement of radial velocities with the highest accuracy currently available. It is fiber-fed by the Cassegrain focus of the 3.6 m telescope in La Silla. HARPS was installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003.
HARPS was developped by a Consortium headed by the Geneva Observatory and composed of the Observatoire de Haute-Provence, the Physikalisches Institut der Universität Bern and the Service d’Aéronomie, Paris. 3)
The instrument is built to obtain very high long term radial velocity accuracy (on the order of 1 m/s). To achieve this goal, HARPS is designed as an echelle spectrograph fed by a pair of fibers and optimized for mechanical stability. It is contained in a vacuum vessel to avoid spectral drift due to temperature and air pressure variations. One of the two fibers collects the star light, while the second is used to either record simultaneously a Th-Ar reference spectrum or the background sky. The two HARPS fibers (object + sky or Th-Ar) have an aperture on the sky of 1" (arcsec); this produces a resolving power of 115,000 in the spectrograph. Both fibers are equipped with an image scrambler to provide a uniform spectrograph pupil illumination, independent of pointing decentering. The spectral range covered is 378nm-691nm, distributed over the echelle orders 89-161. As the detector consists of a mosaic of 2 CCDs (altogether 4k x 4k, 15 µm pixels), one spectral order (N=115, from 530 nm to 533 nm) is lost in the gap between the two chips. 4)
HARPS produces a SNR (Signal-to-Noise Ratio) of 110 per pixel at 550 nm for a Mv=6, G2V star, in 1 minute integration time (1" seeing, airmass = 1.2). When using the Simultaneous Thorium Reference Method (which is the standard mode for achieving the highest accuracy radial velocities) this SNR should be sufficient to achieve a photon noise error on the radial velocity determination of about 0.90 m/s. Taking into account errors introduced by the guiding, focus, and instrumental uncertainties, a global radial velocity accuracy of about 1m/s RMS is achieved. This is attained for spectral type later than G and for non-rotating stars (v sin i < 2 km/s).
In simultaneous Th-Ar mode, HARPS users should strictly follow the calibrations foreseen by the Calibration Plan, which includes a number of bias, flat field and Th-Ar exposures taken before the night.
HARPS is equipped with its own pipeline (installed at La Silla). This pipeline provides the visiting astronomer in near real-time with extracted and wavelength calibrated spectra in all observing modes. When the Simultaneous Thorium reference method is applied, the pipeline delivers precise radial velocities (RV, relative to the solar system barycenter) for late type stars whose RV is known within 1-2km/s, provided that a set of standard calibrations has been executed in the afternoon.
Table 1: Project milestones of HARPS
Table 2: Parameters of the HARPS telescope
Figure 5: The HARPS spectrograph during laboratory tests. The vacuum tank is open so that some of the high-precision components inside can be seen (image credit: ESO)
ESO’s La Silla Observatory is home to one of the most successful planet finders in the history of astronomy: HARPS, or High Accuracy Radial velocity Planet Searcher, which is currently “the” planet hunter of ground-based astronomy. 5)
Attached to the ESO 3.6 m telescope, HARPS searches nightly, and with unparalleled accuracy, for exoplanets. Today it leads the field, regularly generating astounding results that will present fresh challenges for future telescopes like the ELT.
But what does HARPS do to detect these planets? It is all matter of perspective. As we are so far from the stars, we cannot see their exoplanets directly. Instead HARPS detects minute wobbles in the stars’ motion. Stars and their exoplanets are bound together by gravity, so an exoplanet orbits its distant parent star, just as the planets of the Solar System orbit the Sun. But a planet in orbit around a star exerts its own gentle pull, so that the orbital center of the system is a little away from the center of the star and the star itself orbits about this point. We can detect this as a small regular movement of the star to and fro along our line of sight. This tug of war between any star and its exoplanets can be seen (or rather, measured) by HARPS, with an incredible precision. HARPS picks up small changes in the star’s radial velocity (i.e. along the line of sight), which can be as little as a gentle walking pace of 3.5 km/h!
Due to the Doppler effect, this radial velocity change induces a shift of the star’s spectrum towards longer wavelengths as it moves away from us (called redshift) and a shift towards shorter wavelengths (blueshift) as it approaches. This tiny shift in the star’s spectral lines can be measured with a high-precision spectrograph such as HARPS and used to infer the presence of a planet.
For example, in 2011 the team behind HARPS reported the discovery of 50 exoplanets, including 16 new super-Earths (with masses between one and ten times that of the Earth). HARPS, at that time, was responsible for two thirds of all the known exoplanets with masses less than that of Neptune (eso1134). But that's not all! HARPS found the first planet around a star very similar to the Sun (eso1402) and thanks to the observations with this instrument, astronomers have calculated that there are billions of rocky planets in the habitable zones around red dwarfs in the Milky Way (eso1214).
In April 2018 a new small solar telescope called HELIOS — HARPS Experiment for Light Integrated Over the Sun — was installed on the catwalk of the 3.6-meter telescope. HELIOS was built by the University of Geneva and the Centro de Astrofísica da Universidade do Porto. It feeds the HARPS instrument, which is fibre-linked to the 3.6-meter telescope. HARPS is one of the most powerful planet hunters in existence and spends most nights monitoring stars for radial-velocity signals that indicate the presence of exoplanets. During the day HELIOS feeds the sunlight integrated over the solar disk into HARPS to achieve very high precision spectroscopy of the Sun for several hours per day. As well as learning about the Sun itself, the HELIOS project is expected to improve our understanding of stellar activity which turned out to be the main limitation in the detection of Earth-twins using HARPS and therefore will lead to an improvement of exoplanet detection techniques.
MPG/ESO 2.2 meter telescope
The MPG(Max Planck Gesellschaft)/ESO (European Southern Observatory) 2.2 meter telescope was originally constructed by the Max Planck Institute for Astronomy (Heidelberg, Germany) and intended to be sited in Namibia. It was not installed there and later offered to ESO under an agreement where ESO undertook the installation of the telescope at the La Silla Observatory in Chile — achieved in 1983 — and managed its subsequent operation. As of 1 October 2013 ESO no longer offered the telescope to its users, although the Max Planck Society have continued to use it. The telescope and its instruments were also made available to Chilean astronomers and this has continued since 2013. 6)
The telescope currently hosts three instruments: the 67-million pixel WFI (Wide Field Imager) with a field of view as large as the full Moon, which has taken many amazing images of celestial objects; GROND (Gamma-Ray Burst Optical/Near-Infrared Detector), which chases the afterglows of the most powerful explosions in the Universe, known as gamma-ray bursts; and the high-resolution spectrograph, FEROS, used to make detailed studies of stars.
Table 3: Parameters of the MPG/ESO 2.2 m telescope
Figure 6: The MPG/ESO 2.2-meter telescope at La Silla has been in operation since early 1984. Operation and maintenance of the telescope was the responsibility of ESO until September 2013. The telescope (which is a fork mounted Ritchey-Chretien) was built by Zeiss and has been in use at La Silla since 1984. It is equipped with WFI, FEROS and GROND (image credit: ESO/H. H. Heyer) 7)
NTT (New Technology Telescope)
The 3.58-meter NTT ( New Technology Telescope) is a Ritchey-Chretien design of ESO which pioneered the use of active optics. The telescope was inaugurated in 1989. It broke new ground for telescope engineering and design and was the first in the world to have a computer-controlled main mirror. 8)
The NTT is an alt-az telescope. It resides in a rotating building; the control room was moved to a new building located close to the bottom of the NTT ramp in 2003, so now the observers don't rotate with the telescope any longer.
The main mirror is flexible and its shape is actively adjusted by actuators during observations to preserve the optimal image quality. The secondary mirror position is also actively controlled in three directions. This technology, developed by ESO, known as active optics, is now applied to all major modern telescopes, such as the VLT (Very Large Telescope) at Cerro Paranal and the future ELT (Extremely Large Telescope).
Table 4: Some parameters of the NTT
Figure 7: The sun sets behind the New Technology Telescope (NTT) at ESO's La Silla observation site. La Silla, in the southern part of the Atacama desert of Chile, was ESO's first observation site. Home to ESO 3.6-meter telescope and the 3.58-meter New Technology Telescope (NTT), the site sits 2400 m above sea level, creating excellent viewing conditions for astronomers. La Silla also hosts many national telescopes, including the Swiss 1.2-meter Leonhard Euler Telescope and the Danish 1.54-metere telescope (image credit: ESO, Iztok Boncina)
Status and some imagery of La Silla telescopes
• 03 July 2019: Montage of images captured during the total solar eclipse on 2 July 2019, from ESO's La Silla Observatory in Chile, South America. 9)
Figure 8: The images show the progression of the eclipse as the Moon moves in front of the Sun from Earth's perspective and away again. The moment where the Moon is directly in front of the Sun (center image) is known as totality (image credit: ESA/CESAR/Wouter van Reeven)
• 02 July 2019: At 16:40 CLT (Chile Standard Time), the Moon covered the face of the Sun, in a total solar eclipse visible from a 150-km-wide swathe of northern Chile, including ESO’s La Silla Observatory, which celebrated half a century of astronomical research this year. 10)
Figure 9: On 2 July 2019, the path of totality of a solar eclipse passed across ESO’s La Silla Observatory. This rare astronomical event falls in the fiftieth year of operation of ESO’s first observatory. Inaugurated in 1969, La Silla Observatory led Europe to the front line of astronomical research and continues to deliver remarkable science. A thousand visitors, including the President of the Republic of Chile, journeyed to the remote observatory to witness the unique conjunction (image credit: ESO)
- ESO, in collaboration with the Government of Chile, organized an outreach campaign that gave people the opportunity to experience this rare phenomenon from La Silla Observatory itself. A thousand visitors had access to the site, including more than 30 high school students and 30 senior citizens from La Serena, La Higuera and Coquimbo, the districts neighboring the Observatory.
- Another group of students came to La Silla from all over Chile. The youngsters were selected through a contest organized in collaboration with the Chilean Ministry of Education. The students had to write a letter where they explained their interest in science and, particularly, in astronomy. The winners, each together with a parent, were rewarded with a fully paid trip to La Silla.
- International and local media were also invited and about 60 representatives responded to the call. In addition, ESO broadcast the eclipse online.
- Eight social media users were selected from 300 participants from ESON countries to participate in the #MeetESO second edition, a social media gathering taking the winners to all of ESO’s sites. They are sharing their experience with the world on Twitter and Instagram, as well as on their own channels. A public competition dedicated to La Silla Observatory’s 50th anniversary, #LaSilla50Years, also saw one person from ESO’s Member States win a trip to Chile to visit our sites.
- “People around the world made the voyage to Chile, hoping for an unrivalled view of the solar corona as the Moon passed between the Earth and the Sun, turning day into night for almost two minutes,” explains Claudio Melo, ESO Representative in Chile. “These visitors were rewarded with pristine Chilean skies and a perfect view of the solar eclipse.”
- Joining the many visitors at La Silla was the President of the Republic of Chile, Sebastián Piñera, who was welcomed by ESO’s Director General, Xavier Barcons.
- “We are delighted that the President chose to join us at La Silla on this very special day,” said Xavier Barcons. “The eclipse happened on the 50th anniversary of La Silla, an occasion to celebrate the strong and productive partnership between Chile and ESO. La Silla has played an extremely important role in the development of astronomy in Europe and Chile, and Chilean astronomers routinely use telescopes in La Silla for their scientific research.”
- La Silla has been an ESO stronghold since the 1960s. Here, ESO operates two of the most productive 4-meter-class telescopes in the world.
- The 3.58-meter New Technology Telescope (NTT) broke new ground in telescope engineering and design and was the first in the world to have a computer-controlled main mirror (active optics), technology developed at ESO and now applied to most of the world's current large telescopes.
- The ESO 3.6 meter telescope is now home to the world's foremost extrasolar planet hunter in a ground-based observatory: the High Accuracy Radial velocity Planet Searcher (HARPS), a spectrograph with unrivalled precision.
- The President enjoyed a tour of La Silla’s facilities. “We are stardust,” exclaimed the President during the event. “Today Chile is the world capital of astronomy and for this reason to be at La Silla Observatory today is very special.”
- The observatory’s regular astronomical inhabitants were also on site to take advantage of existing observing infrastructure in novel ways. Seven projects with scientific or outreach goals took place during the eclipse, with some using pre-existing telescopes at La Silla, such as the NTT, ExTrA, TAROT and REM, and others using temporary setups. This follows a long tradition of using eclipses for scientific observations, such as the famous confirmation of General Relativity which took place 100 years ago.
- The partial eclipse started at 15:23:50 CLT, with totality lasting 1 minute and 52 seconds from the La Silla summit, between 16:39:23 CLT and 16:41:15 CLT. The partial eclipse ended at 17:47:16 CLT, shortly before sunset.
- As the eclipse itself only occurred during the late afternoon, for the rest of the day visitors enjoyed a wide range of different activities, from tours of the La Silla telescopes to an engaging variety of talks, music and workshops. ESO astronomers and guides were on hand to engage with visitors throughout the day.
- “Witnessing a total solar eclipse is a breathtaking experience that stays with you forever. Fond memories of today’s event will remain in the hearts of our numerous guests at La Silla. This has been a unique moment in this unique observatory’s history,” concluded Xavier Barcons.
- The last total solar eclipse visible from La Silla took place at the end of the 16th century, and the next will not be until the year 2231.
• 15 November 2017: A team working with ESO’s HARPS (High Accuracy Radial velocity Planet Searcher) at the La Silla Observatory in Chile, has found that the red dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Ross 128 is the “quietest” nearby star to host such a temperate exoplanet. 11)
- “This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations,” explains Nicola Astudillo-Defru (Geneva Observatory – University of Geneva, Switzerland), who co-authored the discovery paper.
- Red dwarfs are some of the coolest, faintest — and most common — stars in the Universe. This makes them very good targets in the search for exoplanets and so they are increasingly being studied. In fact, lead author Xavier Bonfils (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, Grenoble, France), named their HARPS program 'The shortcut to happiness', as it is easier to detect small cool siblings of Earth around these stars, than around stars more similar to the Sun.
Figure 10: Artist’s impression of the planet Ross 128 b, a Milky Way star. A temperate Earth-sized planet has been discovered only 11 light-years from the Solar System by a team using ESO’s unique planet-hunting HARPS instrument. The new world has the designation Ross 128 b and is now the second-closest temperate planet to be detected after Proxima b. It is also the closest planet to be discovered orbiting an inactive red dwarf star, which may increase the likelihood that this planet could potentially sustain life. Ross 128 b will be a prime target for ESO’s Extremely Large Telescope, which will be able to search for biomarkers in the planet's atmosphere (image credit: ESO/M. Kornmesser)
- Many red dwarf stars, including Proxima Centauri, are subject to flares that occasionally bathe their orbiting planets in deadly ultraviolet and X-ray radiation. However, it seems that Ross 128 is a much quieter star, and so its planets may be the closest known comfortable abode for possible life.
- Although it is currently 11 light-years from Earth, Ross 128 is moving towards us and is expected to become our nearest stellar neighbor in just 79,000 years — a blink of the eye in cosmic terms. Ross 128 b will by then take the crown from Proxima b and become the closest exoplanet to Earth!
- With the data from HARPS, the team
found that Ross 128 b orbits 20 times closer than the Earth orbits the
Sun. Despite this proximity, Ross 128 b receives only 1.38 times more
irradiation than the Earth. As a result, Ross 128 b’s equilibrium
temperature is estimated to lie between -60 and 20°C, thanks to the
cool and faint nature of its small red dwarf host star, which has just
over half the surface temperature of the Sun. While the scientists
involved in this discovery consider Ross 128b to be a temperate planet,
uncertainty remains as to whether the planet lies inside, outside, or
on the cusp of the habitable zone, where liquid water may exist on a planet’s surface.
- Astronomers are now detecting more
and more temperate exoplanets, and the next stage will be to study
their atmospheres, composition and chemistry in more detail. Vitally,
the detection of biomarkers such as oxygen in the very closest
exoplanet atmospheres will be a huge next step, which ESO’s Extremely Large Telescope (ELT) is in prime position to take.
- “New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterization. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterize a large fraction of these planets,” concludes Xavier Bonfils.
• 10 February 2016: The glowing region in this new image (Figure 11) from the MPG/ESO 2.2-meter telescope is a reflection nebula known as IC 2631. These objects are clouds of cosmic dust that reflect light from a nearby star into space, creating a stunning light show like the one captured here. IC 2631 is the brightest nebula in the Chamaeleon Complex, a large region of gas and dust clouds that harbors numerous newborn and still-forming stars. The complex lies about 500 light-years away in the southern constellation of Chamaeleon. 12)
- IC 2631 is illuminated by the star HD 97300, one of the youngest — as well as most massive and brightest — stars in its neighborhood. This region is full of star-making material, which is made evident by the presence of dark nebulae noticeable above and below IC 2631 in this picture. Dark nebulae are so dense with gas and dust that they prevent the passage of background starlight.
- Reflection nebula, like the one spawned by HD 97300, merely scatter starlight back out into space. Starlight that is more energetic, such as the ultraviolet radiation pouring forth from very hot new stars, can ionize nearby gas, making it emit light of its own. These emission nebulae indicate the presence of hotter and more powerful stars, which in their maturity can be observed across thousands of light-years. HD 97300 is not so powerful, and its moment in the spotlight is destined not to last.
Figure 11: A newly formed star lights up the surrounding cosmic clouds in this image from ESO’s La Silla Observatory in Chile. Dust particles in the vast clouds that surround the star HD 97300 diffuse its light, like a car headlight in enveloping fog, and create the reflection nebula IC 2631. Although HD 97300 is in the spotlight for now, the very dust that makes it so hard to miss heralds the birth of additional, potentially scene-stealing, future stars (image credit: ESO)
• 30 August 2010: The image of Figure 12 was taken with the EFOSC2 (ESO Faint Object Spectrograph and Camera version 2) instrument, attached to the 3.58-meter NTT (New Technology Telescope) at ESO's La Silla Observatory in Chile. The data were acquired through three different filters (B, V, and R) for a total exposure time of 4440 seconds. The field of view is about 4 arcminutes. 13)
Figure 12: NGC 5426 and NGC 5427 are two spiral galaxies of similar sizes engaged in a dramatic dance. It is not certain that this interaction will end in a collision and ultimately a merging of the two galaxies, although the galaxies have already been affected. Together known as Arp 271, this dance will last for tens of millions of years, creating new stars as a result of the mutual gravitational attraction between the galaxies, a pull seen in the bridge of stars already connecting the two. Located 90 million light-years away towards the constellation of Virgo (the Virgin), the Arp 271 pair is about 130 000 light-years across. It was originally discovered in 1785 by William Herschel. Quite possibly, our own Milky Way will undergo a similar collision in about five billion years with the neighboring Andromeda galaxy, which is now located about 2.6 million light-years away from the Milky Way (image credit: ESO)
• 25 February 2009: The Helix Nebula, NGC 7293, lies about 700 light-years away in the constellation of Aquarius (the Water Bearer). It is one of the closest and most spectacular examples of a planetary nebula. These exotic objects have nothing to do with planets, but are the final blooming of Sun-like stars before their retirement as white dwarfs. Shells of gas are blown off from a star’s surface, often in intricate and beautiful patterns, and shine under the harsh ultraviolet radiation from the faint, but very hot, central star. The main ring of the Helix Nebula is about two light-years across or half the distance between the Sun and its closest stellar neighbor. 14)
- Despite being photographically very spectacular the Helix is hard to see visually as its light is thinly spread over a large area of sky and the history of its discovery is rather obscure. It first appears in a list of new objects compiled by the German astronomer Karl Ludwig Harding in 1824. The name Helix comes from the rough corkscrew shape seen in the earlier photographs.
- Although the Helix looks very much like a doughnut, studies have shown that it possibly consists of at least two separate discs with outer rings and filaments. The brighter inner disc seems to be expanding at about 100,000 km/h and to have taken about 12,000 years to have formed.
- Because the Helix is relatively close — it covers an area of the sky about a quarter of the full Moon — it can be studied in much greater detail than most other planetary nebulae and has been found to have an unexpected and complex structure. All around the inside of the ring are small blobs, known as “cometary knots”, with faint tails extending away from the central star. They look remarkably like droplets of liquid running down a sheet of glass. Although they look tiny, each knot is about as large as our Solar System. These knots have been extensively studied, both with the ESO Very Large Telescope and with the NASA/ESA Hubble Space Telescope, but remain only partially understood. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. Some of these seem to be gathered in separate galaxy groups scattered over various parts of the image.
Figure 13: This color-composite image (Figure 13) of the Helix Nebula (NGC 7293) was created from images obtained using the Wide Field Imager (WFI), an astronomical camera attached to the 2.2 m MPG /ESO telescope at the La Silla observatory in Chile. The blue-green glow in the center of the Helix comes from oxygen atoms shining under effects of the intense ultraviolet radiation of the 120 000 degree Celsius central star and the hot gas. Further out from the star and beyond the ring of knots, the red color from hydrogen and nitrogen is more prominent. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. This image was created from images through blue, green and red filters and the total exposure times were 12 minutes, 9 minutes and 7 minutes, respectively (image credit: ESO)
• 25 April 2007: Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbor a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses. 15)
- This exoplanet - as astronomers call planets around a star other than the Sun - is the smallest ever found up to now and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581, is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! The planet's name is Gliese 581 c.
- "We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stéphane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or fully covered with oceans," he adds.
- "Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X."
- The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class.
- "Red dwarfs are ideal targets for the search for low-mass planets where water could be liquid. Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Planets lying in this zone are then more easily detected with the radial-velocity method, the most successful in detecting exoplanets.
Figure 14: Artist's impression of the planetary system around the red dwarf Gliese 581. Using the instrument HARPS on the ESO 3.6 m telescope, astronomers have uncovered 3 planets, all of relative low-mass: 5, 8 and 15 Earth masses. The five Earth-mass planet (seen in foreground - Gliese 581 c) makes a full orbit around the star in 13 days, the other two in 5 (the blue, Neptunian-like planet - Gliese 581 b) and 84 days (the most remote one, Gliese 581 d), image credit: ESO
1) ”La Silla Observatory, ESO's first observatory,” ESO, URL:
2) ”About La Silla,” ESO, URL: http://www.eso.org/sci/facilities/lasilla/site/aboutls.html
5) ”High Accuracy Radial velocity Planet Searcher,” URL: https://www.eso.org/public/teles-instr/lasilla/36/harps/
6) ”MPG/ESO 2.2-meter telescope,” ESO, URL: https://www.eso.org/public/teles-instr/lasilla/mpg22/
8) ”New Technology Telescope,” ESO, URL: https://www.eso.org/public/teles-instr/lasilla/ntt/
9) ”Stages of a total solar eclipse,” ESA, 03 July 2019, URL: http://www.esa.int/spaceinimages/Images/2019/07/Stages_of_a_total_solar_eclipse
11) ”Closest Temperate World Orbiting Quiet Star Discovered, ESO’s HARPS instrument finds Earth-mass exoplanet around Ross 128,” eso1736 — Science Release, 15 November 2017, URL: https://www.eso.org/public/news/eso1736/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).