A recent analysis of Kepler data suggests that planets that orbit very close to their stars can have habitable zones of a few hundred kilometres, and can even support liquid water.
The findings come from a new model that looks at the orbits of Kepler-62b, the last of the ten Kepler-type planets that are not yet in the habitable zone.
Kepler-62 was spotted by the telescope in late 2016, and the team then began using the telescope’s software to analyse its data to figure out whether the planets were likely to be rocky or gaseous.
This new model, published in the Astrophysical Journal Letters, suggests that the orbits should be similar for Kepler-63, Kepler-66 and Kepler-77, the next two planets in the Kepler-family, as well as Kepler-72.
However, it also suggests that there are still a number of planets that have orbits that are very close or even too close to the stars to be habitable.
“The main limitation of the Kepler mission was its relatively small sample size and its limited precision.
Now we have an even better set of observations from our new data and can start to address some of these questions,” said co-author Eric Smith of the University of Oxford, who worked on the project.
These planets are all small, with orbits that only extend about 30 per cent of the time they would be expected to, Smith told New Scientist.
“This gives us a much better idea of what the planets are made of and how they are rotating,” he said.
But while the new models may provide more insight into the planets’ composition, they don’t explain why Kepler-65b, Kepler.66, Kepler 73 and Kepler 80 all orbit so close to stars that they are potentially habitable.
“The planets are the only ones in the whole Kepler family that are orbiting so close that they could potentially be habitable,” said Dr Sarah Bannister, from the University at Buffalo, New York, who was not involved in the study.
“I think it’s a little bit of a paradox.
The Kepler mission is a really good idea, but it has been a little too successful.
And I think that we’re probably missing a whole lot of planets in this part of the galaxy.”
While the model might help answer some of the questions that have puzzled astronomers about the existence of habitable planets, it is still unclear what this means for the future of the mission.
“It’s kind of like an experiment that’s been running on a computer that’s never run on the real thing,” said Smith.
“We still don’t know how many planets there are in the universe, but we do know that there’s a lot of space out there.
There’s a really large amount of space, and there’s no reason why Kepler can’t get there, but there’s also a huge amount of other stuff that we can’t know about.
So we’re still working out what it means for Kepler, what we’re looking for.”
And even if there are many more planets than the 10 known in the Kepler family, we still have some time to learn about them.
“If you look at the numbers of exoplanets, we’re actually not all that far off from what we would expect to see if we were to find more of these planets, because Kepler-59b is in a position where it’s pretty much at the limit,” Smith said.
“The other planets that we might see that are around that range are probably going to be much closer to the star.”
Keylinks will continue to work, with new missions being launched to study planets around distant stars.