Exoplanet has a comet-like tail - Gliese 436b
Exoplanet has a comet-like tail Gliese 436b
Jun 24, 2015
by Deborah Byrd in » Science Wire, Space
A Neptune-sized exoplanet is being trailed by an immense cloud of hydrogen. This discovery might also suggest a method for detecting extrasolar oceans.
Astronomers are keenly interested in finding exoplanets – distant planets orbiting stars besides our sun – that have oceans. That’s because life as we know it on Earth needs water. Today (June 24, 2015), an international team of scientists announced their discovery of a Neptune-sized exoplanet being trailed by an immense cloud of hydrogen. They say that this comet-like tail from an exoplanet helps explain how hot and rocky super-Earths form and may also suggest a method for detecting extrasolar oceans. What’s more, they say, they can use the discovery to get a picture of the future of Earth’s atmosphere, four billion years from now. Their study is published in the journal Nature.
David Sing of the University of Exeter’s Physics and Astronomy department co-authored the study. ...
The exoplanet is known to astronomers GJ436b, or Gliese 436b. Astronomers discovered it in 2004, and it wasn’t until later they realized that this planet transits, or periodically passes in front of its star as seen from Earth. These transits are what enabled astronomers to figure out that Gliese 436b’s atmosphere is leaving behind a gigantic trail of hydrogen.
The star is a red dwarf (Gliese 436), 33 light-years away, and about half the diameter of our sun. The Neptune-sized planet moves in orbit around this star in only three days. It’s some 33 times closer to its star than Earth is to our sun. And thus the star heat’s the planet’s atmosphere to the point that the atmosphere expands and escapes the planet’s gravitational attraction. In other words, the planet is losing its atmosphere to space. If the star were bigger and radiated light more strongly, it might blow the planet’s atmosphere completely away. But this star is some 4 times fainter than our sun. And so it lets the planet’s evaporating atmosphere form a giant cloud surrounding and trailing the planet, much like a comet.
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