An analysis of thousands of stars in the Kepler space telescope’s database, found 95 possible planets orbiting red dwarfs. Of these, three are Earth-sized candidates in the habitable zone – the region around a star where liquid water can exist. Statistically, that means 6 per cent of all red dwarfs in our galaxy should have rocky planets in the habitable zone.
Most of the stars nearest to us are red dwarfs, including the closest, Proxima Centauri. Based on the distribution of red dwarfs in the Milky Way, Dressing estimates that a potentially habitable planet is only 13 light years away.
Due to orbital geometries, the odds that a given planet transits its star so that we can see it are just 1 in 50, so there’s a chance the nearest habitable world will not be one that surveys like Kepler can see. The odds are better that we can see a habitable planet transit within 100 light years of Earth. That’s still near enough for planned observatories to check its atmosphere for gases produced by life on Earth, such as a large amount of oxygen.
NASA is currently considering two planet-hunting telescopes that could help find such a nearby world: the Transiting Exoplanet Survey Satellite (TESS) and the Fast Infrared Exoplanet Spectroscopy Survey Explorer (FINESSE). One of these missions is expected to be selected this spring for launch in 2017.
Even if neither space mission goes ahead, large telescopes on the ground should also be able to detect gases like oxygen in exoplanet atmospheres. Ignas Snellen of the University of Leiden in the Netherlands and colleagues think that, once a habitable planet around a red dwarf is found, planned facilities such as the European Extremely Large Telescope could detect such gases in its atmosphere within three to four years.
“We could be in the business of studying the atmospheres of habitable worlds 10 years from now,” says David Charbonneau, also of the Harvard-Smithsonian Centre for Astrophysics. If NASA launches the missions the space telescopes and we get lucky with analysis of Kepler data to confirm exoplanets, then we could be studying the atmospheres by 2017 or 2020 with space or ground based systems.
The Giant Magellan Telescope (GMT) is a ground-based extremely large telescope planned for completion in 2020. It will consist of seven 8.4 m (27.6 ft) diameter primary segments, with the resolving power of a 24.5 m (80.4 ft) primary mirror and collecting area equivalent to a 21.4 m (70.2 ft) one. The telescope is expected to have over four times the light-gathering ability of existing instruments. Two mirrors are cast and the mountain is being prepared
The Transiting Exoplanet Survey Satellite (TESS) will discover thousands of exoplanets in orbit around the brightest stars in the sky. In a two-year survey, TESS will monitor more than 500,000 stars for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar types and orbital distances. No ground-based survey can achieve this feat. A large fraction of TESS target stars will be 30-100 times brighter than those observed by Kepler satellite, and therefore TESS . planets will be far easier to characterize with follow-up observations. TESS will make it possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. TESS will provide prime targets for observation with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes of the future.
The next step in our study of exoplanets is to study their atmospheres…FINESSE – the Fast Infrared Exoplanet Spectroscopy Survey Explorer – is the first mission dedicated to characterizing the diverse and rapidly growing exoplanet family. Proposed for launch in 2017 as part of the NASA Explorers program, the two-year mission would probe the atmospheres of more than 200 transiting exoplanets using an Earth-orbiting telescope equipped with a highly-stable infrared spectrograph. FINESSE would explore a variety of newly discovered worlds, ranging from hot Jupiter-like planets to super Earths, with repeated detections of important molecules over the course of each planet’s orbit.
The payload for the solar-powered FINESSE spacecraft would consist of a telescope with a 76-centimeter (30-inch) wide aperture attached to single science instrument. The instrument consists of a spectrometer and a guidance sensor (for precision pointing), plus electronics to control and operate both.
The FINESSE spectrometer is the single most important component of the mission. While the telescope collects and focuses light from a star, the spectrometer splits the light into its component wavelengths, called a spectrum. Each chemical in an exoplanet’s atmosphere has a unique spectral signature – like a fingerprint – that scientists can identify by carefully examining spectra collected by FINESSE.
Known as an Offner spectrometer, the design of the FINESSE detector is derived from the Moon Mineralogy Mapper (M3) instrument, which was designed at NASA’s Jet Propulsion Laboratory and flew to the Moon aboard India’s Chandrayaan-1 spacecraft.
SOURCES – New Scientist, NASA
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