Orb hidden in distant dust is 'infant' Neptune-size planet

Date:
June 24, 2020
Source:
University of Hawaii at Manoa
Summary:
The discovery could help astronomers understand how planets like
Earth form and evolve.



FULL STORY ========================================================================== Astronomers study stars and planets much younger than the Sun to learn
about past events that shaped the Solar System and Earth. Most of these
stars are far enough away to make observations challenging, even with
the largest telescopes.

But now this is changing.


========================================================================== University of Hawai'i at Manoa astronomers are part of an international
team that recently discovered an infant planet around a nearby young
star. The discovery was reported Wednesday in the international journal
Nature.

The planet is about the size of Neptune, but, unlike Neptune, it is much
closer to its star, taking only eight and a half days to complete one
orbit. It is named "AU Mic b" after its host star, AU Microscopii, or
"AU Mic" for short.

The planet was discovered using the NASA TESS planet-finding satellite,
as it periodically passed in front of AU Mic, blocking a small fraction
of its light.

The signal was confirmed by observations with another NASA satellite,
the Spitzer Space Telescope, and with the NASA Infrared Telescope
Facility (IRTF) on Maunakea. The observations on Hawai'i Island used a
new instrument called iSHELL that can make very precise measurements of
the motion of a star like AU Mic. These measurements revealed a slight
wobble of the star, as it moves in response to the gravitational pull of
the planet. It confirmed that AU Mic b was a planet and not a companion
star, which would cause a much larger motion.

Discovery on Maunakea sets foundation AU Mic and its planet are about 25 million years young, and in their infancy, astronomically speaking. AU
Mic is also the second closest young star to Earth.

It is so young that dust and debris left over from its formation still
orbit around it. The debris collides and breaks into smaller dust
particles, which orbit the star in a thin disk. This disk was detected
in 2003 with the UH 88- inch telescope on Maunakea. The newly-discovered
planet orbits within a cleared-out region inside the disk.

"This is an exciting discovery, especially as the planet is in one
of the most well-known young star systems, and the second-closest to
Earth. In addition to the debris disk, there is always the possibility
of additional planets around this star. AU Mic could be the gift that
keeps on giving," said Michael Bottom, an Assistant Astronomer at the
UH Institute for Astronomy.

"Planets, like people, change as they mature. For planets this means
that their orbits can move and the compositions of their atmospheres
can change. Some planets form hot and cool down, and unlike people,
they would become smaller over time. But we need observations to test
these ideas and planets like AU Mic b are an exceptional opportunity,"
said Astronomer Eric Gaidos, a professor in the Department of Earth
Sciences at UH M?noa.

Clues to the origin of Earth-like planets AU Mic is not only much younger
than the Sun, it is considerably smaller, dimmer and redder. It is a
"red dwarf," the most numerous type of star in the galaxy. The TESS
satellite is also discovering Earth-sized and possibly habitable planets
around older red dwarfs, and what astronomers learn from AU Mic and AU
Mic b can be applied to understand the history of those planets.

"AU Mic b, and any kindred planets that are discovered in the
future, will be intensely studied to understand how planets form
and evolve. Fortuitously, this star and its planet are on our cosmic
doorstep. We do not have to venture very far to see the show," Gaidos explained. He is a co-author on another five forthcoming scientific publications that have used other telescopes, including several on
Maunakea, to learn more about AU Mic and its planet.

AU Mic appears low in the summer skies of Hawai'i but you'll need
binoculars to see it. Despite its proximity, the fact that it is a dim
red star means it is too faint to be seen with the unaided eye.


========================================================================== Story Source: Materials provided by University_of_Hawaii_at_Manoa. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Plavchan, P., Barclay, T., Gagne', J. et al. A planet within
the debris
disk around the pre-main-sequence star AU Microscopii. Nature,
2020 DOI: 10.1038/s41586-020-2400-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200624120448.htm

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