12 ASTRONOMY • APRIL 2021
QUANTUM GRAVITY
An exoplanet circling two stars
336 light-years away may provide
clues about where a long-sought world
may be hiding in our own solar system.
This strange exoplanet, HD106906 b,
was first discovered in 2013 with the
Magellan Telescopes at the Las Campanas
Observatory in Chile’s Atacama Desert.
But in order to determine its orbit,
astronomers needed the Hubble Space
Telescope’s clarity and precision. Eleven
times the mass of Jupiter, HD106906 b lies
more than 730 times the average Earth-
Sun separation from its two host stars. At
such an incredible distance, it takes the
planet 15,000 years to complete one orbit.
Not only is HD106906 b remote for an
exoplanet, but its orbit is also tilted 30°
from the orbital plane of the dusty disc
surrounding its host stars.
“To highlight why this is weird, we can
just look at our own solar system and
see that all of the planets lie roughly in
the same plane,” said study leader Meiji
Nguyen in a press release.
It’s possible that HD106906 b formed
much closer to its twin host stars, but
as it traveled through the debris disksurrounding the stars, its orbit decayed.
The whirling twin stars then kicked the
planet further out into the system when
it migrated too close. The planet was
almost entirely ejected from the system,
but astronomers think a passing star
might have stabilized the planet’s distant
orbit. Candidates for such an interloper
have been identified using the European
Space Agency’s Gaia survey satellite.
Some researchers suspect a similar
scenario may have played out in our
own solar system, paving the way for
the hypothetical Planet Nine. The gravi-
tational inf luence of such a planet could
explain the strange orbits of a unique
group of Kuiper Belt objects beyond
Neptune.
Planet Nine has yet to be discovered
(or even proved to exist). But HD106906 b
provides a compelling parallel to the way
researchers predict Planet Nine could
orbit our Sun. Using the upcoming James
Webb Space Telescope, astronomers hope
to gather more data on HD106906 b to
better understand it, with the goal of
finding more planets in similar orbits
around other stars. — C.B.Far-flung exoplanet resembles
long-sought Planet Nine
In what may be the longest-exposure
photograph ever taken, this image
captures the path of the Sun over
2,953 days — more than eight years
— at the University of Hertfordshire’s
Bayfordbury Observatory in the U.K.
But a high-tech detector didn’t take
this record-setting image — it was a
humble beer can lined with photo-
graphic paper, acting as a low-tech
pinhole camera. Regina Valkenborgh,
a master of fine arts student, placed
the beer can on the side of a telescope
dome in 2012 — where it sat, forgotten,
for eight years, until an observatory
staff member removed it in September 2020. The resulting image of the Sun’s trail arcing across the sky is a solargraph, recording
when the Sun was visible and when it was obscured by cloudy weather. — M.Z.Eight-year Sun trail imaged with beer can
MIRROR WORLD. HD106906 b occupies an
unlikely orbit around its binary host stars
336 light-years away, perhaps providing clues
to where the hypothesized Planet Nine may lie
in our own neighborhood. ESA/HUBBLE, M. KORNMESSERREGINA^
VALK
ENBORGH/
UNIVERSITYO
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