Investigating the potential for life around the galaxy's smallest stars
New telescope will see planetary neighbors' atmospheres

Date:
September 29, 2021
Source:
University of California - Riverside
Summary:
When the world's most powerful telescope launches into space
this year, scientists will learn whether Earth-sized planets
in our 'solar neighborhood' have a key prerequisite for life --
an atmosphere.



FULL STORY ==========================================================================
When the world's most powerful telescope launches into space this
year, scientists will learn whether Earth-sized planets in our 'solar neighborhood' have a key prerequisite for life -- an atmosphere.


========================================================================== These planets orbit an M-dwarf, the smallest and most common type of
star in the galaxy. Scientists do not currently know how common it is
for Earth-like planets around this type of star to have characteristics
that would make them habitable.

"As a starting place, it is important to know whether small, rocky planets orbiting M-dwarfs have atmospheres," said Daria Pidhorodetska, a doctoral student in UC Riverside's Department of Earth and Planetary Sciences. "If
so, it opens up our search for life outside our solar system." To help
fill this gap in understanding, Pidhorodetska and her team studied whether
the soon-to-launch James Webb Space Telescope, or the currently-in- orbit Hubble Space Telescope, are capable of detecting atmospheres on these
planets. They also modeled the types of atmospheres likely to be found,
if they exist, and how they could be distinguished from each other. The
study has now been published in the Astronomical Journal.

Study co-authors include astrobiologists Edward Schwieterman and Stephen
Kane from UCR, as well as scientists from Johns Hopkins University,
NASA's Goddard Space Flight Center, Cornell University and the University
of Chicago.

The star at the center of the study is an M-dwarf called L 98-59, which measures only 8% of our sun's mass. Though small, it is only 35 light
years from Earth. It's brightness and relative closeness make it an
ideal target for observation.



========================================================================== Shortly after they form, M-dwarfs go through a phase in which they can
shine two orders of magnitude brighter than normal. Strong ultraviolet radiation during this phase has the potential to dry out their orbiting planets, evaporating any water from the surface and destroying many
gases in the atmosphere.

"We wanted to know if the ablation was complete in the case of the two
rocky planets, or if those terrestrial worlds were able to replenish
their atmospheres," Pidhorodetska said.

The researchers modeled four different atmospheric scenarios: one in which
the L 98-59 worlds are dominated by water, one in which the atmosphere
is mainly composed of hydrogen, a Venus-like carbon dioxide atmosphere,
and one in which the hydrogen in the atmosphere escaped into space,
leaving behind only oxygen and ozone.

They found that the two telescopes could offer complementary information
using transit observations, which measure a dip in light that occurs as a planet passes in front of its star. The L 98-59 planets are much closer
to their star than Earth is to the sun. They complete their orbits in
less than a week, making transit observations by telescope faster and
more cost effective than observing other systems in which the planets
are farther from their stars.

"It would only take a few transits with Hubble to detect or rule out a hydrogen- or steam-dominated atmosphere without clouds," Schwieterman
said.

"With as few as 20 transits, Webb would allow us to characterize gases
in heavy carbon dioxide or oxygen-dominated atmospheres." Of the four atmospheric scenarios the researchers considered, Pidhorodetska said
the dried-out oxygen-dominated atmosphere is the most likely.



==========================================================================
"The amount of radiation these planets are getting at that distance from
the star is intense," she said.

Though they may not have atmospheres that lend themselves to life today,
these planets can offer an important glimpse into what might happen to
Earth under different conditions, and what might be possible on Earth-like worlds elsewhere in the galaxy.

The L 98-59 system was only discovered in 2019, and Pidhorodetska said
she is excited to get more information about it when Webb is launched
later this year.

"We're on the precipice of revealing the secrets of a star system that
was hidden until very recently," Pidhorodetska said.

========================================================================== Story Source: Materials provided by
University_of_California_-_Riverside. Original written by Jules
Bernstein. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Daria Pidhorodetska, Sarah E. Moran, Edward W. Schwieterman, Thomas
Barclay, Thomas J. Fauchez, Nikole K. Lewis, Elisa V. Quintana,
Geronimo L. Villanueva, Shawn D. Domagal-Goldman, Joshua
E. Schlieder, Emily A.

Gilbert, Stephen R. Kane, Veselin B. Kostov. L 98-59:
A Benchmark System of Small Planets for Future Atmospheric
Characterization. The Astronomical Journal, 2021; 162 (4): 169 DOI:
10.3847/1538-3881/ac1171 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210929092634.htm

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