By Ryan Whitwam
The last few decades of astronomical research have resulted
in the discovery of thousands of probable exoplanets, but seldom have
we been able to identify smaller planets like Earth. Even more rare is
actual visual evidence of a smaller exoplanet.
Researchers using the Atacama Large Millimeter/submillimeter Array
(ALMA) may have observed just that. The team has released a new image of
the nearby star TW Hydrae showing what appears to be a gap created by
the formation of an Earth-like planet around this young star.
Most exoplanet observations are based on the transit method —
telescopes watch for small drops in light output from stars as planets
pass in front of them. Astronomers can also detect small wobbles in
stars caused by the orbiting of massive objects like planets. The new
ALMA images are a result of listening for the faint radio emissions from
dust and gas in orbit of TW Hydrae.
TW Hydrae offers astronomers a unique opportunity to learn
about alien solar systems for several reasons. For one, it’s rather
close by astronomical standards, just 175 light years. Our
current-generation telescopes can capture this star in amazing detail.
It’s also very young, having formed about 10 million years ago. That
means it’s still dim and has a large protoplanetary disc of gas
surrounding it. The disc is also oriented face-on toward Earth, so
astronomers can see an entire undistorted view of TW Hydrae as it forms.
The new image of TW Hydrae
shows several dark bands in the protoplanetary disc believed to be
evidence of planets forming. The two most prominent are easily spotted
in the image above, but they’re much farther out than Earth. Compared
with our solar system, the first ring would be at about the orbit of
Uranus and the second is near that of Pluto. The most important ring is
magnified in the image below, and is at roughly the same distance from
TW Hydrae as Earth is from the sun. That could be a future Earth or a
super-Earth.
Further study of TW Hydrae could help us better understand
the formation and history of our own solar system, but it might take
some time before ALMA’s impressive new images are improved upon. The
team used ALMA’s high-resolution, long-baseline configuration with all
the array’s dishes at their maximum separation of 15 kilometers. It will
be some time before another instrument can top it. Finding more
protoplanetary discs at later stages of development could offer
additional insights.
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