As many as six billion Earth-like planets in our galaxy, according to
new estimates

Date:
June 16, 2020
Source:
University of British Columbia
Summary:
There may be as many as one Earth-like planet for every five
Sun-like stars in the Milky Way Galaxy, according to new estimates.



FULL STORY ========================================================================== [Exoplanet illustration | Credit: (c) Sko'rzewiak / stock.adobe.com]
Exoplanet illustration (stock image).

Credit: (c) Sko'rzewiak / stock.adobe.com [Exoplanet illustration |
Credit: (c) Sko'rzewiak / stock.adobe.com] Exoplanet illustration
(stock image).

Credit: (c) Sko'rzewiak / stock.adobe.com Close There may be as many as
one Earth-like planet for every five Sun-like stars in the Milky way
Galaxy, according to new estimates by University of British Columbia astronomers using data from NASA's Kepler mission.


==========================================================================
To be considered Earth-like, a planet must be rocky, roughly Earth-sized
and orbiting Sun-like (G-type) stars. It also has to orbit in the
habitable zones of its star -- the range of distances from a star in
which a rocky planet could host liquid water, and potentially life,
on its surface.

"My calculations place an upper limit of 0.18 Earth-like planets per
G-type star," says UBC researcher Michelle Kunimoto, co-author of the new
study in The Astronomical Journal. "Estimating how common different kinds
of planets are around different stars can provide important constraints
on planet formation and evolution theories, and help optimize future
missions dedicated to finding exoplanets." According to UBC astronomer
Jaymie Matthews: "Our Milky Way has as many as 400 billion stars, with
seven per cent of them being G-type. That means less than six billion
stars may have Earth-like planets in our Galaxy." Previous estimates of
the frequency of Earth-like planets range from roughly 0.02 potentially habitable planets per Sun-like star, to more than one per Sun- like star.

Typically, planets like Earth are more likely to be missed by a
planet search than other types, as they are so small and orbit so far
from their stars. That means that a planet catalogue represents only
a small subset of the planets that are actually in orbit around the
stars searched. Kunimoto used a technique known as 'forward modelling'
to overcome these challenges.

"I started by simulating the full population of exoplanets around
the stars Kepler searched," she explained. "I marked each planet as
'detected' or 'missed' depending on how likely it was my planet search algorithm would have found them. Then, I compared the detected planets to
my actual catalogue of planets. If the simulation produced a close match,
then the initial population was likely a good representation of the actual population of planets orbiting those stars." Kunimoto's research also
shed more light on one of the most outstanding questions in exoplanet
science today: the 'radius gap' of planets. The radius gap demonstrates
that it is uncommon for planets with orbital periods less than 100 days
to have a size between 1.5 and two times that of Earth. She found that
the radius gap exists over a much narrower range of orbital periods than previously thought. Her observational results can provide constraints
on planet evolution models that explain the radius gap's characteristics.

Previously, Kunimoto searched archival data from 200,000 stars of NASA's
Kepler mission. She discovered 17 new planets outside of the Solar
System, or exoplanets, in addition to recovering thousands of already
known planets.


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


========================================================================== Journal Reference:
1. Michelle Kunimoto, Jaymie M. Matthews. Searching the Entirety
of Kepler
Data. II. Occurrence Rate Estimates for FGK Stars. The Astronomical
Journal, 2020; 159 (6): 248 DOI: 10.3847/1538-3881/ab88b0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200616100831.htm

--- up 21 weeks, 2 hours, 34 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)