The star 51 Pegasi in the constellation of Pegasus
Wide-field view of the sky around the star 51 Pegasi
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New technique paints promising picture for future
Astronomers using the HARPS
planet-hunting machine at ESO’s La Silla Observatory in Chile have made
the first-ever direct detection of the spectrum of visible light
reflected off an exoplanet. These observations also revealed new
properties of this famous object, the first exoplanet ever discovered
around a normal star: 51 Pegasi b. The result promises an exciting
future for this technique, particularly with the advent of next
generation instruments, such as ESPRESSO, on the VLT, and future
telescopes, such as the E-ELT.
The exoplanet 51 Pegasi b [1] lies some 50 light-years from Earth in the constellation of Pegasus.
It was discovered in 1995 and will forever be remembered as the first
confirmed exoplanet to be found orbiting an ordinary star like the Sun [2]. It is also regarded as the archetypal hot Jupiter
— a class of planets now known to be relatively commonplace, which are
similar in size and mass to Jupiter, but orbit much closer to their
parent stars.
Since that landmark discovery, more than 1900 exoplanets in 1200
planetary systems have been confirmed, but, in the year of the twentieth
anniversary of its discovery, 51 Pegasi b returns to the ring once more
to provide another advance in exoplanet studies.
The team that made this new detection was led by Jorge Martins from the Instituto de Astrofísica e Ciências do Espaço (IA) and the Universidade do Porto, Portugal, who is currently a PhD student at ESO in Chile. They used the HARPS instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile.
Currently, the most widely used method to examine an exoplanet’s
atmosphere is to observe the host star’s spectrum as it is filtered
through the planet’s atmosphere during transit — a technique known as
transmission spectroscopy. An alternative approach is to observe the
system when the star passes in front of the planet, which primarily
provides information about the exoplanet’s temperature.
The new technique does not depend on finding a planetary transit, and
so can potentially be used to study many more exoplanets. It allows the
planetary spectrum to be directly detected in visible light,
which means that different characteristics of the planet that are
inaccessible to other techniques can be inferred.
The host star’s spectrum is used as a template to guide a search for a
similar signature of light that is expected to be reflected off the
planet as it describes its orbit. This is an exceedingly difficult task
as planets are incredibly dim in comparison to their dazzling parent
stars.
The signal from the planet is also easily swamped by other tiny effects and sources of noise [3].
In the face of such adversity, the success of the technique when
applied to the HARPS data collected on 51 Pegasi b provides an extremely
valuable proof of concept.
Jorge Martins explains: “This type of detection technique is of
great scientific importance, as it allows us to measure the planet’s
real mass and orbital inclination, which is essential to more fully
understand the system. It also allows us to estimate the planet’s
reflectivity, or albedo, which can be used to infer the composition of
both the planet’s surface and atmosphere.”
51 Pegasi b was found to have a mass about half that of Jupiter’s and
an orbit with an inclination of about nine degrees to the direction to
the Earth [4].
The planet also seems to be larger than Jupiter in diameter and to be
highly reflective. These are typical properties for a hot Jupiter that
is very close to its parent star and exposed to intense starlight.
HARPS was essential to the team’s work, but the fact that the result was obtained using the ESO 3.6-metre telescope,
which has a limited range of application with this technique, is
exciting news for astronomers. Existing equipment like this will be
surpassed by much more advanced instruments on larger telescopes, such
as ESO’s Very Large Telescope and the future European Extremely Large Telescope [5].
"We are now eagerly awaiting first light of the ESPRESSO
spectrograph on the VLT so that we can do more detailed studies of this
and other planetary systems,” concludes Nuno Santos, of the IA and Universidade do Porto, who is a co-author of the new paper.
Notes
[1] Both 51 Pegasi b and its host star 51 Pegasi are among the objects available for public naming in the IAU’s NameExoWorlds contest.
[3] The challenge is similar to trying
to study the faint glimmer reflected off a tiny insect flying around a
distant and brilliant light.
[4] This means that the planet’s orbit
is close to being edge on as seen from Earth, although this is not
close enough for transits to take place.
[5] ESPRESSO
on the VLT, and later even more powerful instruments on much larger
telescopes such as the E-ELT, will allow for a significant increase in
precision and collecting power, aiding the detection of smaller
exoplanets, while providing an increase in detail in the data for
planets similar to 51 Pegasi b.
More Information
This research was presented in a paper “Evidence for a spectroscopic
direct detection of reflected light from 51 Peg b”, by J. Martins et
al., to appear in the journal Astronomy & Astrophysics on 22 April 2015.
The team is composed of J. H. C. Martins (IA and Universidade do
Porto, Porto, Portugal; ESO, Santiago, Chile), N. C. Santos (IA and
Universidade do Porto), P. Figueira (IA and Universidade do Porto), J.
P. Faria (IA and Universidade do Porto), M. Montalto (IA and
Universidade do Porto), I. Boisse (Aix Marseille Université, Marseille,
France), D. Ehrenreich (Observatoire de Genève, Geneva, Switzerland), C.
Lovis (Observatoire de Genève), M. Mayor (Observatoire de Genève), C.
Melo (ESO, Santiago, Chile), F. Pepe (Observatoire de Genève), S. G.
Sousa (IA and Universidade do Porto), S. Udry (Observatoire de Genève)
and D. Cunha (IA and Universidade do Porto).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
Links
Contacts
Jorge Martins
Instituto de Astrofísica e Ciências do Espaço/Universidade do Porto
Porto, Portugal
Tel: +56 2 2463 3087
Email: Jorge.Martins@iastro.pt
Nuno Santos
Instituto de Astrofísica e Ciências do Espaço/Universidade do Porto
Porto, Portugal
Tel: +351 226 089 893
Email: Nuno.Santos@iastro.pt
Stéphane Udry
Observatoire de l’Université de Genève
Geneva, Switzerland
Tel: +41 22 379 24 67
Email: stephane.udry@unige.ch
Isabelle Boisse
Aix Marseille Université
Marseille, France
Email: Isabelle.Boisse@lam.fr
Richard Hook
ESO Public Information Officer
Garching, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Instituto de Astrofísica e Ciências do Espaço/Universidade do Porto
Porto, Portugal
Tel: +56 2 2463 3087
Email: Jorge.Martins@iastro.pt
Nuno Santos
Instituto de Astrofísica e Ciências do Espaço/Universidade do Porto
Porto, Portugal
Tel: +351 226 089 893
Email: Nuno.Santos@iastro.pt
Stéphane Udry
Observatoire de l’Université de Genève
Geneva, Switzerland
Tel: +41 22 379 24 67
Email: stephane.udry@unige.ch
Isabelle Boisse
Aix Marseille Université
Marseille, France
Email: Isabelle.Boisse@lam.fr
Richard Hook
ESO Public Information Officer
Garching, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source:ESO
