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EI2GYB > ASTRO 29.08.21 10:56l 167 Lines 8659 Bytes #999 (0) @ WW
BID : 13837_EI2GYB
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Subj: Are we missing other Earths?
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Sent: 210829/0853Z @:EI2GYB.DGL.IRL.EURO #:13837 BPQ6.0.22
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Are we missing other Earths?
Some exoplanet searches could be missing nearly half of the Earth-sized
planets around other stars. New findings suggest that Earth-sized worlds
could be lurking undiscovered in binary star systems, hidden in the glare
of their parent stars.
As roughly half of all stars are in binary systems, this means that
astronomers could be missing many Earth-sized worlds.
Some exoplanet searches could be missing nearly half of the Earth-sized
planets around other stars.
New findings from a team using the international Gemini Observatory and
the WIYN 3.5-meter Telescope at Kitt Peak National Observatory suggest
that Earth-sized worlds could be lurking undiscovered in binary star s
ystems, hidden in the glare of their parent stars.
As roughly half of all stars are in binary systems, this means that
astronomers could be missing many Earth-sized worlds.
Earth-sized planets may be much more common than previously realized.
Astronomers working at NASA Ames Research Center have used the twin
telescopes of the international Gemini Observatory, a Program of NSF's
NOIRLab, to determine that many planet-hosting stars identified by NASA's
TESS exoplanet-hunting mission [1] are actually pairs of stars --
known as binary stars -- where the planets orbit one of the stars in the pair.
After examining these binary stars, the team has concluded that
Earth-sized planets in many two-star systems might be going unnoticed by
transit searches like TESS's, which look for changes in the light from a
star when a planet passes in front of it [2].
The light from the second star makes it more difficult to detect the
changes in the host star's light when the planet transits.
The team started out by trying to determine whether some of the exoplanet
host stars identified with TESS were actually unknown binary stars.
Physical pairs of stars that are close together can be mistaken for single
stars unless they are observed at extremely high resolution.
So the team turned to both Gemini telescopes to inspect a sample of
exoplanet host stars in painstaking detail.
Using a technique called speckle imaging [3], the astronomers set out to
see whether they could spot undiscovered stellar companions.
Using the `Alopeke and Zorro instruments on the Gemini North and South
telescopes in Chile and Hawai'i, respectively, [4] the team observed
hundreds of nearby stars that TESS had identified as potential exoplanet hosts.
They discovered that 73 of these stars are really binary star systems
that had appeared as single points of light until observed at higher
resolution with Gemini.
"With the Gemini Observatory's 8.1-meter telescopes, we obtained extremely
high-resolution images of exoplanet host stars and detected stellar
companions at very small separations," said Katie Lester of NASA's Ames
Research Center, who led this work.
Lester's team also studied an additional 18 binary stars previously found
among the TESS exoplanet hosts using the NN-EXPLORE Exoplanet and Stellar
Speckle Imager (NESSI) on the WIYN 3.5-meter Telescope at Kitt Peak
National Observatory, also a Program of NSF's NOIRLab.
After identifying the binary stars, the team compared the sizes of
the detected planets in the binary star systems to those in single-star
systems. They realized that the TESS spacecraft found both large and small
exoplanets orbiting single stars, but only large planets in binary systems.
These results imply that a population of Earth-sized planets could be
lurking in binary systems and going undetected using the transit
method employed by TESS and many other planet-hunting telescopes.
Some scientists had suspected that transit searches might be missing
small planets in binary systems, but the new study provides observational
support to back it up and shows which sizes of exoplanets are affected [5].
"We have shown that it is more difficult to find Earth-sized planets in
binary systems because small planets get lost in the glare of their two
parent stars," Lester stated. "Their transits are 'filled in' by the
light from the companion star," added Steve Howell of NASA's Ames
Research Center, who leads the speckle imaging effort and was involved
in this research.
"Since roughly 50% of stars are in binary systems, we could be missing
the discovery of -- and the chance to study -- a lot of Earth-like planets,"
Lester concluded.
The possibility of these missing worlds means that astronomers will need
to use a variety of observational techniques before concluding that a
given binary star system has no Earth-like planets. "Astronomers need
to know whether a star is single or binary before they claim that no
small planets exist in that system," explained Lester.
"If it's single, then you could say that no small planets exist.
But if the host is in a binary, you wouldn't know whether a small planet
is hidden by the companion star or does not exist at all.
You would need more observations with a different technique to figure
that out."
As part of their study, Lester and her colleagues also analyzed how
far apart the stars are in the binary systems where TESS had detected
large planets.
The team found that the stars in the exoplanet-hosting pairs were
typically farther apart than binary stars not known to have planets [6].
This could suggest that planets do not form around stars that have close
stellar companions.
"This speckle imaging survey illustrates the critical need for NSF
telescope facilities to characterize newly discovered planetary systems
and develop our understanding of planetary populations," said National
Science Foundation Division of Astronomical Sciences Program Officer
Martin Still.
"This is a major finding in exoplanet work," Howell commented.
"The results will help theorists create their models for how planets form and
evolve in double-star systems."
Notes
[1] TESS is the Transiting Exoplanet Survey Satellite, a NASA mission
designed to search for planets orbiting other stars in a survey of
around 75% of the entire night sky. The mission launched in 2018 and has
detected more than 3500 candidate exoplanets, of which more than 130 have
been confirmed.
The satellite looks for exoplanets by observing their host stars; a
transiting exoplanet causes a subtle but measurable dip in the brightness
of its host star as it crosses in front of the star and blocks some of its
light.
[2] The transit technique is one way of discovering exoplanets.
It involves looking for regular decreases in the light of a star that could
be caused by a planet passing in front of or "transiting" the star and
blocking some of the starlight.
[3] Speckle imaging is an astronomical technique that allows astronomers to
see past the blur of the atmosphere by taking many quick observations in
rapid succession.
By combining these observations, it is possible to cancel out the blurring
effect of the atmosphere, which affects ground-based astronomy by causing
stars in the night sky to twinkle.
[4] `Alopeke & Zorro are identical imaging instruments permanently mounted
on the Gemini North and South telescopes. Their names mean "fox" in Hawaiian
and Spanish, respectively, reflecting their respective locations on Maunakea
in Hawai?i and on Cerro Pach¢n in Chile.
[5] The team found that planets twice the size of Earth or smaller could not
be detected using the transit method when observing binary systems.
[6] Lester's team found that the exoplanet-hosting binary stars they
identified had average separations of about 100 astronomical units.
(An astronomical unit is the average distance between the Sun and Earth.)
Binary stars that are not known to host planets are typically separated
by around 40 astronomical units.
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