Artist's impression of the rocky super-Earth HD 85512 b -
one of more than 50 new exoplanets found by HARPS (Image: ESO/M.
Kornmesser)
The European Southern Observatory (ESO) has announced its
exoplanet-hunting HARPS (High Accuracy Radial velocity Planet
Searcher) has discovered 50 new exoplanets, making it the
largest amount of exoplanets that has been announced at the one
time. Bringing the number of planets discovered outside our
solar system to 645, the 50-planet haul includes 16 super-Earths
(planets with a mass between one and ten times that of Earth),
including one that orbits at the edge of the habitable zone of
its star.
Whereas NASA's
Kepler spacecraft looks for fluctuations in the brightness
of stars to detect planets passing in front of it, HARPS is a
high precision echelle spectrograph that observes Doppler shifts
in the spectrum of the star around which a planet orbits. In
contrast to the majority of planets discovered by the transit
method employed by Kepler, which are very distant from us, the
planets found by HARPS are around stars that are much closer,
making them better targets for many kinds of additional
follow-up observations.
HARPS discovered its first super-Earth in the habitable zone,
(Gliese
581 d), in 2007. More recently, it was also used to
demonstrate that the other candidate super-Earth in the
habitable zone around star Gliese 581 (Gliese
581 g) doesn't exist.
In the eight years since HARPS achieved first light, its
observations have allowed astronomers to improve the estimate of
how likely it is that a star like the Sun is host to low-mass
planets as opposed to gaseous giants. By studying the properties
of all the HARPS planets discovered so far, the team has found
that about 40 percent of stars similar to the Sun have at least
one planet lighter than Saturn. Additionally, the majority of
exoplanets of Neptune mass or less appear to be in systems with
multiple planets.
With upgrades to both hardware and software, the team is
increasing the sensitivity of HARPS, to search for rocky planets
that could support life. One potential candidate is the newly
discovered HD 85512 b, which is estimated to be just 3.6 times
the mass of the Earth and is located at the edge of the
habitable zone where water may be present in liquid form if
conditions are right.
"This is the lowest-mass confirmed planet discovered by the
radial velocity method that potentially lies in the habitable
zone of its star, and the second low-mass planet discovered by
HARPS inside the habitable zone," says Lisa Kaltenegger of the
Max Planck Institute for Astronomy and Harvard Smithsonian
Center for Astrophysics.
The team says that HARPS is now so sensitive that it can
detect radial velocity amplitudes of significantly less than 4
km/h (2.5 mph), allowing it to detect planets under two Earth
masses. Earth induces a 0.32 km/h (0.2 mph) radial velocity on
the Sun.
HARPS is currently installed on ESO's 3.6 m Telescope at La
Silla Observatory in Chile but a copy of HARPS is to be
installed on the Telescopio Nazionale Galileo in the Canary
Islands, to survey stars in the northern sky. Additionally, a
new and more powerful planet-finder, called ESPRESSO, (Echelle
SPectrograph for Rocky Exoplanet and Stable Spectroscopic
Observations), will be installed on ESO's Very Large Telescope
in Chile in 2016. It will boast radial velocity precision of
0.35 km/h (0.22 mph) or less, giving it the ability to discover
Earth-mass planets in the habitable zone of low-mass stars.
"In the coming ten to twenty years we should have the first
list of potentially habitable planets in the Sun's neighborhood.
Making such a list is essential before future experiments can
search for possible spectroscopic signatures of life in the
exoplanet atmospheres," concludes Michel Mayor, who leads the
ESO's HARPS
team.
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