Sky & Telescope - July 2023 - 11

ESO / M. KORNMESSER
INTERSTELLAR OBJECTS
'Oumuamua's Odd Behavior,
Explained
AN ASTROCHEMIST and an astronomer
may have just explained the
unusual orbit of the interstellar visitor
1I/'Oumuamua (S&T: Oct. 2018, p. 20).
Jennifer Bergner (University of California,
Berkeley) and Darryl Seligman
(Cornell University) propose that the
object was emitting hydrogen picked
up during its time between the stars,
offering a relatively simple explanation
to a puzzle that has previously prompted
some outlandish claims.
The true nature of 'Oumuamua,
discovered in 2017, wasn't immediately
obvious. It resembled a pancake in
shape, and although initially classified
as a comet, it didn't have a visible tail or
coma. One thing that did make it more
comet-like was the way it was decelerating
as it went away from the Sun; that
IN BRIEF
Prebiotic Compounds on
Ryugu
Prebiotic compounds previously found in
meteorites, such as uracil (one of the four
nucleobases in RNA) and niacin (vitamin B3),
have now turned up in pristine samples from
the asteroid 162173 Ryugu, confirming their
extraterrestrial origin. While meteorite analysis
over the last decade has suggested that
compounds essential for life exist in space,
these space rocks can pick up contaminants
as they fall to Earth. On the other hand,
the sample that Japan's Hayabusa 2 probe
carefully collected during its visit to Ryugu
should have little terrestrial contamination.
Yasuhiro Oba (Hokkaido University, Japan),
who previously found prebiotics in meteorites,
led a team in using the same technique
on the asteroid samples. The team reports
March 21st in Nature Communications that
uracil is present at a level of parts per billion
in two samples taken from Ryugu. While this
concentration is lower than previously found
in some other meteorites, Oba says that
might be because the parent bodies of the
meteorites and of Ryugu experienced different
chemical histories.
¢JEFF HECHT
Read more about the discovery at
https://is.gd/Ryuguprebiotics.
is, it slowed on its way out, but not in
the way expected if only gravity were in
play. But without any signs of cometary
activity, the normal mechanism behind
such motion didn't seem to fit.
Bergner and Seligman put forward
a straightforward scenario in the
March 23rd Nature. Cosmic radiation
cooked the comet as it traveled through
interstellar space, Bergner explains. As
cosmic rays penetrated tens of meters
into the ice, they converted 20 to 30%
of the water molecules (H2O) into
molecular hydrogen (H2). This trapped
hydrogen was then released when the
Sun warmed the comet.
Bergner and Seligman found that
such outgassing is negligible for most
comets. It only powered 'Oumuamua
because this object was so small, and
astronomers on Earth wouldn't have
seen any associated activity.
" It probably won't settle all debate
around this object, " says Alan Fitzsim2028
Launch for Rosalind
Franklin Rover
The Rosalind Franklin rover, part of the
European Space Agency (ESA) ExoMars
program, has weathered delays due to
technical issues, the COVID-19 pandemic,
and the Russia-Ukraine War. On March 13th,
ESA announced a " rebirth " for the mission,
with a new launch date: October 2028. A
looping trajectory will put the rover on Mars
two years later, during spring in the planet's
northern hemisphere. Originally, Russia
was going to provide the Proton rocket
that would have brought the rover to Mars,
as well as the Kazachok lander that would
have delivered the rover to the Martian
surface. However, due to Russia's invasion
of Ukraine, ESA formally terminated the mission's
cooperation with the nation's space
agency, Roscosmos, in July 2022. Europe
is now building its own lander, which will
no longer carry a science package. NASA,
which was originally part of ExoMars but
pulled out in 2012, is stepping in again, too.
The U.S. agency has requested $30 million
to support the mission in FY2024; the agencies
are still working out longer-term costs.
In addition to providing landing-engine elements,
NASA could also provide launch services
and radioisotope heater units, required
to keep the rover warm during cold Martian
nights. In the meantime, an infusion of 500
Artist's illustration of 1I/'Oumuamua
mons (Queen's University Belfast),
who was not involved in the research,
" but it provides a coherent picture of
'Oumuamua based on current knowledge,
without resorting to exotic or even
fanciful theories. "
Fitzsimmons thinks we could see this
mechanism play out in small comets
from the Oort Cloud. With facilities
like the Rubin Observatory and the
Extremely Large Telescope due to see
first light in the next five years, we may
not have to wait too long for answers.
¢COLIN STUART
million euros ($540 million) over the next
three years from ESA's governing Ministerial
Council will keep the project afloat.
¢DAVID DICKINSON
New Planets in Our
Neighborhood
A planet-hunting consortium that designed
the CARMENES instrument on the 3.5-meter
telescope at the Calar Alto Observatory in
Spain has released data on more than 50
worlds within 65 light-years of Earth. The
consortium published visible-light observations
of more than 350 stars in the February
Astronomy & Astrophysics (additional
near-infrared observations are forthcoming).
The catalog includes the discovery of 33 new
planets, confirmation of 26 planets found in
previous transit surveys, and re-analysis of 17
known planets. Crunching the statistics, project
scientist Ignasi Ribas (Institute of Space
Studies of Catalonia, Spain) and colleagues
find that there are 1.4 planets for every star,
consistent with the occurrence rate found by
the Kepler mission. Four of the new planets
are likely rocky and in their stars' habitable
zones, meaning they could host liquid water
on their surfaces. On the other end of the
spectrum, the team also found gas giants
orbiting extremely low-mass stars, challenging
planet-formation models.
¢ ARWEN RIMMER
sk yand tele scope .o r g * JULY 2023 11
https://www.is.gd/Ryuguprebiotics http://skyandtelescope.org
Sky & Telescope - July 2023

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