NASA’s Hubble Space Telescope has looked for evidence of
atmospheres around several earth-sized planets in the
TRAPPIST-1 system, including three that are in the star’s
habitable zone, where liquid water could exist on the
surface. A lot of astronomers and space enthusiasts were very
excited by the discovery of the seven Earth-sized planets of the
TRAPPIST-1 system. The planets orbit an ultracool dwarf star
about 40 light-years away. Scientists have theories about
what these planets may be like and whether they could support
life, but we won’t know for sure until we get more comprehensive
observations of this system, including data on the planets’
atmospheres. As a planet in the TRAPPIST-1 system passes between
us and the star, it blocks out a small portion of the star’s
light. Telescopes like Hubble can look at changes in specific
wavelengths of light, which provide clues to the composition
and size of the planet's atmosphere. Hubble observations
in May, 2016 of TRAPPIST-1 b and c showed that these planets do
not seem to have thick, puffy hydrogen-rich atmospheres. This
indicates a higher chance that they are rocky, terrestrial
planets rather than mini-gas-giants. Hubble then
observed planets d, e, f, and g in December 2016 and January
2017 in near-infrared wavelengths, and the results
were similar. Hubble found no sign of thick, puffy
hydrogen-rich atmospheres for any of the four planets. The
data suggest that there isn’t this gas-giant-like atmosphere
for planets d, e, and f. The data from this round of
observations was not as strong for planet g, so while there’s
no evidence for a thick hydrogen-rich atmosphere on g,
the researchers are not yet ruling it out. Planets e, f, and
g orbit at distances where temperatures would allow for
liquid water, while d is likely a little too hot. Hubble has yet
to take observations of planet h, which is outside the system’s
habitable zone. To summarize – Hubble has not seen evidence of
thick, hydrogen-rich atmospheres for planets b, c, d, e, and f,
and of those five planets, e and f are in the habitable zone.
Planet g needs more data, and Hubble has not yet looked at
planet h. It’s worth noting though, that even the planets
outside the habitable zone still might be able to have liquid
water somewhere on its surface in certain conditions. It’s also
worth noting that if any of these planets have high-altitude
clouds and hazes, that would block Hubble’s ability to detect
a thick, hydrogen-rich atmosphere, but such an
atmosphere is not likely to exist on these planets. Many
possibilities remain for what types of atmospheres these
planets have, or whether they even have atmospheres. The
TRAPPIST-1 planets could have compact atmospheres similar to
Mars, Venus, Earth, or something entirely different. Researchers
hope to use Hubble’s ultraviolet capabilities to look for
evidence of water vapor or methane, and NASA’s upcoming
James Webb Space Telescope will look in the far-infrared to
further characterize these atmospheres. Future telescopes
also hope to look for hints of whether the planets are
habitable and if life could be present. The TRAPPIST-1 system
provides the best opportunity we currently have to study
Earth-size exoplanets. Over the next few years, Hubble and other
telescopes will work together, each contributing important
observations. For the first time ever, we’ll have an in-depth
understanding of a set of terrestrial planets outside our
solar system.
www.nasa.gov/hubble @NASAHubble