Astronomers discover last three planets Kepler telescope observed before
going dark

Date:
May 30, 2023
Source:
Massachusetts Institute of Technology
Summary:
With the help of citizen scientists, astronomers discovered what
may be the last three planets that the Kepler Space Telescope saw
before it was retired.


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FULL STORY ==========================================================================
More than 5,000 planets are confirmed to exist beyond our solar
system. Over half were discovered by NASA's Kepler Space Telescope,
a resilient observatory that far outlasted its original planned
mission. Over nine and a half years, the spacecraft trailed the Earth,
scanning the skies for periodic dips in starlight that could signal the presence of a planet crossing in front of its star.

In its last days, the telescope kept recording the brightness of stars
as it was running out of fuel. On Oct. 30, 2018, its fuel tanks depleted,
the spacecraft was officially retired.

Now, astronomers at MIT and the University of Wisconsin at Madison,
with the help of citizen scientists, have discovered what may be the
last planets that Kepler gazed upon before going dark.

The team combed through the telescope's last week of high-quality data
and spotted three stars, in the same part of the sky, that appeared to
dim briefly.

The scientists determined that two of the stars each host a planet,
while the third hosts a planet "candidate" that has yet to be verified.

The two validated planets are K2-416 b, a planet that is about 2.6 times
the size of the Earth and that orbits its star about every 13 days,
and K2-417 b, a slightly larger planet that is just over three times
Earth's size and that circles its star every 6.5 days. For their size and proximity to their stars, both planets are considered "hot mini-Neptunes
." They are located about 400 light years from Earth.

The planet candidate is EPIC 246251988 b -- the largest of the three
worlds at almost four times the size of the Earth. This Neptune-sized
candidate orbits its star in around 10 days, and is slightly farther away, 1,200 light years from Earth.

"We have found what are probably the last planets ever discovered
by Kepler, in data taken while the spacecraft was literally running
on fumes," says Andrew Vanderburg, assistant professor of physics
in MIT's Kavli Institute for Astrophysics and Space Research. "The
planets themselves are not particularly unusual, but their atypical
discovery and historical importance makes them interesting." The team
has published their discovery today in the journal Monthly Notices of
the Royal Astronomical Society. Vanderburg's co-authors are lead author
Elyse Incha, at the University of Wisconsin at Madison, and amateur
astronomers Tom Jacobs and Daryll LaCourse, along with scientists at
NASA, the Center for Astrophysics of Harvard and the Smithsonian, and
the University of North Carolina at Chapel Hill.

Data squeeze In 2009, NASA launched the Kepler telescope into space,
where it followed the Earth's orbit and continuously monitored millions
of stars in a patch of the northern sky. Over four years, the telescope recorded the brightness of over 150,000 stars, which astronomers used
to discover thousands of possible planets beyond our solar system.

Kepler kept observing beyond its original three-and-a-half-year mission,
until May 2013, when the second of four reaction wheels failed. The wheels served as the spacecraft's gyroscopes, helping to keep the telescope
pointed at a particular point in the sky. Kepler's observations were
put on pause while scientists searched for a fix.

One year later, Kepler restarted as "K2," a reworked mission that used
the sun's wind to balance the unsteady spacecraftin a way that kept
the telescope relatively stable for a few months at a time -- a period
called a campaign. K2 went on for another four years, observing over
half a million more stars before the spacecraft finally ran out of fuel
during its 19th campaign. The data from this last campaign comprised
only a week of high-quality observations and another 10 days of noisier measurements as the spacecraft rapidly lost fuel.

"We were curious to see whether we could get anything useful out of this
short dataset," Vanderburg says. "We tried to see what last information
we could squeeze out of it." By eye Vanderburg and Incha presented the challenge to the Visual Survey Group, a team of amateur and professional astronomers who hunt for exoplanets in satellite data. They search by
eye through thousands of recorded light curves of each star, looking
for characteristic dips in brightness that signal a "transit," or the
possible crossing of a planet in front of its star.

The citizen scientists are especially suited to combing through short
datasets such as K2's very last campaign.

"They can distinguish transits from other wacky things like a glitch in
the instrument," Vanderburg says. "That's helpful especially when your
data quality begins to suffer, like it did in K2's last bit of data."
The astronomers spent a few days efficiently looking through the light
curves that Kepler recorded from about 33,000 stars. The team worked
with only a week's worth of high-quality data from the telescope before
it began to lose fuel and focus. Even in this short window of data,
the team was able to spot a single transit in three different stars.

Incha and Vanderburg then looked at the telescope's very last,
lower-quality observations, taken in its last 11 days of operation, to
see if they could spot any additional transits in the same three stars -- evidence that a planet was periodically circling its star.

During this 11-day period, as the spacecraft was losing fuel, its
thrusters fired more erratically, causing the telescope's view to
drift. In their analysis, the team focused on the region of each star's
light curves between thruster activity, to see if they could spot any additional transits in these less data-noisy moments.

This search revealed a second transit for K2-416 b and K2-417 b,
validating that they each host a planet. The team also detected a similar
dip in brightness for K2-417 b in data taken of the same star by NASA's Transiting Exoplanet Survey Satellite (TESS), a mission that is led and operated by MIT.

Data from TESS helped to confirm the planet candidate around this star.

"Those two are pretty much, without a doubt, planets," Incha says. "We
also followed up with ground-based observations to rule out all kinds of
false positive scenarios for them, including background star interference,
and close- in stellar binaries." "These are the last chronologically
observed planets by Kepler, but every bit of the telescope's data is
incredibly useful," Incha says. "We want to make sure none of that data
goes to waste, because there are still a lot of discoveries to be made."
This research was supported, in part, by MIT, NASA, and the University
of Wisconsin Undergraduate Academic Awards.

* RELATED_TOPICS
o Space_&_Time
# Astronomy # Extrasolar_Planets # Stars #
Space_Exploration # Space_Telescopes # NASA # Pluto #
Kuiper_Belt
* RELATED_TERMS
o Spitzer_space_telescope o Uranus'_natural_satellites
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========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennufer
Chu. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Elyse Incha, Andrew Vanderburg, Tom Jacobs, Daryll LaCourse, Allyson
Bieryla, Emily Pass, Steve B Howell, Perry Berlind, Michael Calkins,
Gilbert Esquerdo, David W Latham, Andrew W Mann. Kepler's last
planet discoveries: two new planets and one single-transit candidate
from K2 campaign 19. Monthly Notices of the Royal Astronomical
Society, 2023; 523 (1): 474 DOI: 10.1093/mnras/stad1049 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230530125403.htm

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