Unveiling rogue planets with NASA's Roman Space Telescope

Date:
August 21, 2020
Source:
NASA/Goddard Space Flight Center
Summary:
New simulations show that NASA's Nancy Grace Roman Space Telescope
will be able to reveal myriad rogue planets -- freely floating
bodies that drift through our galaxy untethered to a star.



FULL STORY ==========================================================================
New simulations show that NASA's Nancy Grace Roman Space Telescope will
be able to reveal myriad rogue planets -- freely floating bodies that
drift through our galaxy untethered to a star. Studying these island
worlds will help us understand more about how planetary systems form,
evolve, and break apart.


========================================================================== Astronomers discovered planets beyond our solar system, known as
exoplanets, in the 1990s. We quickly went from knowing of only our own planetary system to realizing that planets likely outnumber the hundreds
of billions of stars in our galaxy. Now, a team of scientists is finding
ways to improve our understanding of planet demographics by searching
for rogue worlds.

"As our view of the universe has expanded, we've realized that our solar
system may be unusual," said Samson Johnson, a graduate student at Ohio
State University in Columbus who led the research effort. "Roman will help
us learn more about how we fit in the cosmic scheme of things by studying
rogue planets." The findings, published in the Astronomical Journal,
center on the Roman Space Telescope's ability to locate and characterize isolated planets. Astronomers have only tentatively discovered a few of
these nomad worlds so far because they are so difficult to detect.

Finding galactic nomads Roman will find rogue planets by conducting a
large microlensing survey.

Gravitational lensing is an observational effect that occurs because
the presence of mass warps the fabric of space-time. The effect is
extreme around very massive objects, like black holes and entire
galaxies. Even solitary planets cause a detectable degree of warping,
called microlensing.



==========================================================================
If a rogue planet aligns closely with a more distant star from our
vantage point, the star's light will bend as it travels through the
curved space-time around the planet. The result is that the planet acts
like a natural magnifying glass, amplifying light from the background
star. Astronomers see the effect as a spike in the star's brightness as
the star and planet come into alignment.

Measuring how the spike changes over time reveals clues to the rogue
planet's mass.

"The microlensing signal from a rogue planet only lasts between a few
hours and a couple of days and then is gone forever," said co-author
Matthew Penny, an assistant professor of physics and astronomy at
Louisiana State University in Baton Rouge. "This makes them difficult
to observe from Earth, even with multiple telescopes. Roman is a
game-changer for rogue planet searches." Microlensing offers the best
way to systematically search for rogue planets - - especially those with
low masses. They don't shine like stars and are often very cool objects, emitting too little heat for infrared telescopes to see.

These vagabond worlds are essentially invisible, but Roman will discover
them indirectly thanks to their gravitational effects on the light of
more distant stars.

Lessons from cosmic castaways Johnson and co-authors showed that
Roman will be able to detect rogue planets with masses as small as
Mars. Studying these planets will help narrow down competing models of planetary formation.



==========================================================================
The planet-building process can be chaotic, since smaller objects
collide with one another and sometimes stick together to form larger
bodies. It's similar to using a piece of playdough to pick up other
pieces. But occasionally collisions and close encounters can be so
violent that they fling a planet out of the gravitational grip of its
parent star. Unless it manages to drag a moon along with it, the newly
orphaned world is doomed to wander the galaxy alone.

Rogue planets may also form in isolation from clouds of gas and dust,
similar to how stars grow. A small cloud of gas and dust could collapse
to form a central planet instead of a star, with moons instead of planets surrounding it.

Roman will test planetary formation and evolution models that predict
different numbers of these isolated worlds. Determining the abundance
and masses of rogue planets will offer insight into the physics that
drives their formation. The research team found that the mission will
provide a rogue planet count that is at least 10 times more precise than current estimates, which range from tens of billions to trillions in our galaxy. These estimates mainly come from observations by ground-based telescopes.

Since Roman will observe above the atmosphere, nearly a million miles
away from Earth in the direction opposite the Sun, it will yield far
superior microlensing results. In addition to providing a sharper view,
Roman's perspective will allow it to stare at the same patch of sky continuously for months at a time. Johnson and his colleagues showed
that Roman's microlensing survey will detect hundreds of rogue planets,
even though it will search only a relatively narrow strip of the galaxy.

Part of the study involved determining how to analyze the mission's
future data to obtain a more accurate census. Scientists will be able
to extrapolate from Roman's rogue planet count to estimate how common
these objects are throughout the entire galaxy.

"The universe could be teeming with rogue planets and we wouldn't
even know it," said Scott Gaudi, a professor of astronomy at Ohio
State University and a co-author of the paper. "We would never find
out without undertaking a thorough, space-based microlensing survey
like Roman is going to do." The Nancy Grace Roman Space Telescope
is managed at Goddard, with participation by NASA's Jet Propulsion
Laboratory and Caltech/IPAC in Pasadena, the Space Telescope Science
Institute in Baltimore, and a science team comprising scientists from
research institutions across the United States.


========================================================================== Story Source: Materials provided
by NASA/Goddard_Space_Flight_Center. Original written by Ashley
Balzer. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* YouTube_video:_How_Gravitational_Microlensing_Reveals_Rogue_Planets ========================================================================== Journal Reference:
1. Samson A. Johnson, Matthew Penny, B. Scott Gaudi, Eamonn Kerins,
Nicholas
J. Rattenbury, Annie C. Robin, Sebastiano Calchi Novati, Calen B.

Henderson. Predictions of the Nancy Grace Roman Space Telescope
Galactic Exoplanet Survey. II. Free-floating Planet Detection
Rates. The Astronomical Journal, 2020; 160 (3): 123 DOI:
10.3847/1538-3881/aba75b ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200821113725.htm

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