The first moon聽orbiting an exoplanet is slowly coming into view. New observations from the Hubble Space Telescope have provided more evidence for an exomoon聽around a distant gas giant 鈥� and if it does exist, it is unlike any moon in the solar system.
In 2017, 快猫短视频 reported that David Kipping and Alex Teachey at Columbia University in New York had spotted a possible exomoon in data from the Kepler Space Telescope, orbiting a distant planet called Kepler-1625b, which is thousands of light years away.
At the time, the data only provided a whiff of a moon 鈥� enough to inspire the researchers to look more closely, but not nearly to call it a discovery.
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鈥淲e鈥檝e had candidates in the past and investigated them, and most of them have evaporated,鈥� Kipping said at the time. But this exomoon candidate has not evaporated. Observations with Hubble showed two hints that it might really be there.
Moon hints
The first was that the planet passed in front of its star 78 minutes earlier than we would expect if it had no moon, indicating that something is dragging on it gravitationally, changing its speed. The second was a second, smaller dip in the star鈥檚 light after the dip caused by the planet passing by, suggesting two objects passing across the star.
These measurements indicate a gas giant about the size of Jupiter, orbited by a moon much bigger than any in our solar system. In fact, the moon seems to be so large that it is difficult to explain with our current understanding of how moons form in the solar system.
鈥淚t will appear two times bigger than Earth鈥檚 moon in the sky,鈥� says Teachey. 鈥淗aving a moon the size of Neptune with a Jupiter-sized planet sort of defies easy explanation.鈥�
Like its planet, the moon is probably a gas giant, and with an average temperature of around 27掳C. If it weren鈥檛 made of gas, that would mean that it could potentially be habitable, but Kipping cautions it is too early to say. 鈥淲e don鈥檛 know very much about the conditions on the moon at all 鈥� we don鈥檛 even know for sure that the moon is there.鈥�
鈥淭hey鈥檝e probably found an exoworld, but whether it鈥檚 an exoplanet or an exomoon I don鈥檛 think they can really be sure about,鈥� says David Waltham at Royal Holloway, University of London. 鈥淲hat they need to do is to make more observations with Hubble.鈥�
Teachey says that the next passage of Kepler-1625b in front of its star is in May 2019. They have requested time on Hubble to observe the star, and are waiting for approval.
Science Advances
