Artist’s impression of the ultracool dwarf star TRAPPIST-1 from the surface of one of its planets
Artist’s impression of the ultracool dwarf star TRAPPIST-1 from close to one of its planets
Artist’s impression of the ultracool dwarf star TRAPPIST-1 and its three planets
The ultracool dwarf star TRAPPIST-1 in the constellation of Aquarius
Comparison between the Sun and the ultracool dwarf star TRAPPIST-1
Videos
ESOcast 83: Ultracool Dwarf with Planets
Artist’s impression of the ultracool dwarf star TRAPPIST-1 from the surface of one of its planets
Artist’s impression of the ultracool dwarf star TRAPPIST-1 from close to one of its planets
Currently the best place to search for life beyond the Solar System
Astronomers using the TRAPPIST telescope
at ESO’s La Silla Observatory have discovered three planets orbiting an
ultracool dwarf star just 40 light-years from Earth. These worlds have
sizes and temperatures similar to those of Venus and Earth and are the
best targets found so far for the search for life outside the Solar
System. They are the first planets ever discovered around such a tiny
and dim star. The new results will be published in the journal Nature on
2 May 2016.
A team of astronomers led by Michaël Gillon, of the Institut d’Astrophysique et Géophysique at the University of Liège in Belgium, have used the Belgian TRAPPIST telescope [1] to observe the star 2MASS J23062928-0502285,
now also known as TRAPPIST-1. They found that this dim and cool star
faded slightly at regular intervals, indicating that several objects
were passing between the star and the Earth [2].
Detailed analysis showed that three planets with similar sizes to the Earth were present.
TRAPPIST-1 is an ultracool dwarf star — it is much cooler
and redder than the Sun and barely larger than Jupiter. Such stars are
both very common in the Milky Way and very long-lived, but this is the
first time that planets have been found around one of them. Despite
being so close to the Earth, this star is too dim and too red to be seen
with the naked eye or even visually with a large amateur telescope. It
lies in the constellation of Aquarius (The Water Carrier).
Emmanuël Jehin, a co-author of the new study, is excited: “This
really is a paradigm shift with regards to the planet population and
the path towards finding life in the Universe. So far, the existence of
such ‘red worlds’ orbiting ultra-cool dwarf stars was purely
theoretical, but now we have not just one lonely planet around such a
faint red star but a complete system of three planets!”
Michaël Gillon, lead author of the paper presenting the discovery, explains the significance of the new findings: "Why
are we trying to detect Earth-like planets around the smallest and
coolest stars in the solar neighbourhood? The reason is simple: systems
around these tiny stars are the only places where we can detect life on
an Earth-sized exoplanet with our current technology. So if we want to
find life elsewhere in the Universe, this is where we should start to
look."
Astronomers will search for signs of life by studying the
effect that the atmosphere of a transiting planet has on the light
reaching Earth. For Earth-sized planets orbiting most stars this tiny
effect is swamped by the brilliance of the starlight. Only for the case
of faint red ultra-cool dwarf stars — like TRAPPIST-1 — is this effect
big enough to be detected.
Follow-up observations with larger telescopes, including the HAWK-I instrument on ESO’s 8-metre Very Large Telescope
in Chile, have shown that the planets orbiting TRAPPIST-1 have sizes
very similar to that of Earth. Two of the planets have orbital periods
of about 1.5 days and 2.4 days respectively, and the third planet has a
less well determined period in the range 4.5 to 73 days.
"With such short orbital periods, the planets are
between 20 and 100 times closer to their star than the Earth to the Sun.
The structure of this planetary system is much more similar in scale to
the system of Jupiter’s moons than to that of the Solar System," explains Michaël Gillon.
Although they orbit very close to their host dwarf star,
the inner two planets only receive four times and twice, respectively,
the amount of radiation received by the Earth, because their star is
much fainter than the Sun. That puts them closer to the star than the habitable zone
for this system, although it is still possible that they possess
habitable regions on their surfaces. The third, outer, planet’s orbit is
not yet well known, but it probably receives less radiation than the
Earth does, but maybe still enough to lie within the habitable zone.
"Thanks to several giant telescopes currently under
construction, including ESO’s E-ELT and the NASA/ESA/CSA James Webb
Space Telescope due to launch for 2018, we will soon be able to study
the atmospheric composition of these planets and to explore them first
for water, then for traces of biological activity. That's a giant step
in the search for life in the Universe," concludes Julien de Wit, a co-author from the Massachusetts Institute of Technology (MIT) in the USA.
This work opens up a new direction for exoplanet hunting,
as around 15% of the stars near to the Sun are ultra-cool dwarf stars,
and it also serves to highlight that the search for exoplanets has now
entered the realm of potentially habitable cousins of the Earth. The
TRAPPIST survey is a prototype for a more ambitious project called SPECULOOS that will be installed at ESO’s Paranal Observatory [3].
Notes
[1] TRAPPIST (the TRAnsiting Planets and PlanetesImals Small Telescope) is a Belgian robotic 0.6-metre telescope operated from the University of Liège and based at ESO’s La Silla Observatory
in Chile. It spends much of its time monitoring the light from around
60 of the nearest ultracool dwarf stars and brown dwarfs (“stars” which
are not quite massive enough to initiate sustained nuclear fusion in
their cores), looking for evidence of planetary transits.The target in
this case, TRAPPIST-1, is an ultracool dwarf, with about 0.05% of the
Sun’s luminosity and a mass of about 8% that of the Sun.
[2] This is one of the main methods
that astronomers use to identify the presence of a planet around a star.
They look at the light coming from the star, to see if some of the
light is blocked as the planet passes in front of its host star on the
line of sight to Earth — transits
the star, as astronomers say. As the planet orbits around its star, we
expect to see regular small dips in the light coming from the star as
the planet moves in front of it.
[3] SPECULOOS is mostly funded by the
European Research Council and led also by the University of Liège. Four
1-metre robotic telescopes will be installed at the Paranal Observatory
to search for habitable planets around 500 ultra-cool stars over the
next five years.
Links
- Research paper
- TRAPPIST is the acronym of "TRAnsiting Planets and PlanetesImals Small Telescope”, more information here and at the TRAPPIST website
- Further information about TRAPPIST-1
- SPECULOOS is the acronym of "Search for habitable Planets EClipsing ULtra-cOOl Stars". For more information, see here
Contacts
Michaël Gillon
University of Liege
Belgium
Tel: +32 43 669 743
Cell: +32 473 346 402
Email: michael.gillon@ulg.ac.be
Julien de Wit
MIT
Cambridge, Massachusetts, USA
Email: jdewit@mit.edu
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
