The Kepler Space Telescope has discovered more than 2,000 exoplanets in our galaxy, exceeding all expectations for the mission. Even after tragic setbacks, this plucky little space telescope has been a boon to science. Yet, it’s days are numbered, according to NASA. Mission managers say they expect Kepler to run out of fuel in the next few months, putting an end to nearly a decade of planet-spotting.
The Kepler mission has operated in two distinct parts. After launch, the satellite started its main scientific observations by scanning large numbers of stars over time. It’s looking for telltale dips in brightness that could indicate an exoplanet has passed in front of the star. This event is known as a transit, and it’s the most reliable method we currently have for detecting planets orbiting other stars.
In order to make its observations, Kepler has to remain pointed at the same cluster of stars for long periods as it floats through space. It did that with the aid of reaction wheels, but two of its reactions wheels had failed by 2013. Unable to maintain orientation, the future of the mission seemed in doubt. We’re still hearing about Kepler discoveries all the time, though. So, what gives?
Kepler has continued as the “K2” mission since 2014, which keeps the telescope pointed at star fields at several points in its orbit by using pressure from the solar wind to stabilize the spacecraft. That’s why Kepler data keeps piling up. It takes time for people (or computers) to go through the candidate signals to determine if they’re really exoplanets.
Kepler expends fuel to get itself pointed in the right direction for each “campaign” of observations. NASA believes the tank will run dry in the next few months. There’s not a true fuel gauge on Kepler, but the team plans to watch for signs like pressure drops in the tank. All they have are estimates, but Kepler’s remaining time is definitely best measured in months now.
Refueling Kepler is not in the cards, either. It’s orbiting some 93 million miles away, and the expense of any such mission would not be worth it. Even with more fuel, Kepler is an ailing spacecraft that will probably encounter more failures in the near future.
When Kepler signs off, that won’t be the end for exoplanet hunting. For one, there are thousands of candidate exoplanets that need to be checked in the giant Kepler backlog. NASA also plans to launch the Transiting Exoplanet Survey Satellite (TESS) next month. This satellite will pick up where Kepler left off by scanning the brightest stars in the sky to learn more about the exoplanets that may lurk there. In the coming years, the James Webb Space Telescope should help us gather more exoplanet information than ever before with its advanced imaging instruments.
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