1706437724
For the first time, water vapor has been found on a relatively small exoplanet. The astronomers who received help from Hubble are very excited, although they don’t yet know exactly what is happening.
At about twice the diameter of Earth, planet GJ 9827d is the smallest planet on which a water-rich atmosphere has been found. It’s evidence that there may be many more small planets with water vapor in our galaxy. GJ 9827d was discovered by the Kepler telescope back in 2017. It orbits a red dwarf star in just over six days. It is 97 light years from Earth.
First time
“This is the first time that we can directly demonstrate that these planets with a water-rich atmosphere actually exist around other stars,” says researcher Björn Benneke from University of Montreal. “This is an important step in studying how often rocky planets have an atmosphere and what its composition is.”
However, it is still too early to say whether Hubble measured a small amount of water vapor in a hydrogen-rich atmosphere or whether the planet’s atmosphere is mostly water, left behind after an ancient hydrogen-helium atmosphere was vaporized by radiation.
Water vapor dominates or not?
“Our observation program was specifically designed with the aim of not only finding the water molecules in the planet’s atmosphere, but also specifically searching for water vapor. “Any result would be great, regardless of whether water vapor is predominant or only slightly present in a hydrogen-rich atmosphere,” says lead researcher Pierre-Alexis Roy from University of Montreal.
Benneke adds: “So far we have not been able to directly measure the atmosphere of such a small planet. Only now is it slowly starting to happen. On such small planets there must be a certain point at which there is no more hydrogen and they get an atmosphere more like that of Venus, i.e. mainly rich in CO2.”
As hot as Venus
Since the planet is as hot as Venus – about 425 degrees Celsius – it would be an inhospitable, steamy world anyway if its atmosphere consisted mostly of water vapor. At this point, researchers are conflicted: the planet still clings to a water vapor-soaked shell, making it a kind of mini-Neptune. Or it is a warmer version of Jupiter’s moon Europa, whose crust contains twice as much water as Earth. “Planet GJ 9827d could be half water and half rock. And on a smaller, rocky interior there can be a lot of water vapor,” says Benneke.
If the planet has a water-rich atmosphere, it would have formed further away from its star, where it is cold enough for water to form ice. In this scenario, the planet would have moved closer to its star later and received more radiation. The hydrogen was then heated and allowed to escape the planet’s weak gravity. The alternative theory is that the planet formed near its star and only traces of water are present in its atmosphere.
De Hubble
The Hubble has put scientists on the trail of water vapor. The space telescope observed the planet for three years, during which it passed in front of its star eleven times. During such a so-called transition, the star’s light is filtered through the planet’s atmosphere and carries a kind of fingerprint of water molecules that Hubble can observe. If there are clouds on the planet, they hang low enough that they don’t completely obscure Hubble’s view.
The next step is to use the even more precise James Webb Telescope with its infrared equipment to further study the atmosphere and examine other molecules present.
#time #water #vapor #atmosphere #small #planet