Some planets may be better for life than Earth

Date:
October 5, 2020
Source:
Washington State University
Summary:
Researchers have identified two dozen planets outside our solar
system that may have conditions more suitable for life than our
own. Some of these orbit stars that may be better than even our sun.



FULL STORY ========================================================================== Earth is not necessarily the best planet in the universe. Researchers
have identified two dozen planets outside our solar system that may
have conditions more suitable for life than our own. Some of these orbit
stars that may be better than even our sun.


==========================================================================
A study led by Washington State University scientist Dirk Schulze-Makuch recently published in the journal Astrobiology details characteristics of potential "superhabitable" planets, that include those that are older,
a little larger, slightly warmer and possibly wetter than Earth. Life
could also more easily thrive on planets that circle more slowly changing
stars with longer lifespans than our sun.

The 24 top contenders for superhabitable planets are all more than
100 light years away, but Schulze-Makuch said the study could help
focus future observation efforts, such as from NASA's James Web Space Telescope, the LUVIOR space observatory and the European Space Agency's
PLATO space telescope.

"With the next space telescopes coming up, we will get more information,
so it is important to select some targets," said Schulze-Makuch,
a professor with WSU and the Technical University in Berlin. "We have
to focus on certain planets that have the most promising conditions for
complex life. However, we have to be careful to not get stuck looking for
a second Earth because there could be planets that might be more suitable
for life than ours." For the study, Schulze-Makuch, a geobiologist
with expertise in planetary habitability teamed up with astronomers Rene
Heller of the Max Planck Institute for Solar System Research and Edward
Guinan of Villanova University to identify superhabitability criteria
and search among the 4,500 known exoplanets beyond our solar system for
good candidates. Habitability does not mean these planets definitely
have life, merely the conditions that would be conducive to life.

The researchers selected planet-star systems with probable terrestrial
planets orbiting within the host star's liquid water habitable zone from
the Kepler Object of Interest Exoplanet Archive of transiting exoplanets.

While the sun is the center of our solar system, it has a relatively
short lifespan of less than 10 billion years. Since it took nearly 4
billion years before any form of complex life appeared on Earth, many
similar stars to our sun, called G stars, might run out of fuel before
complex life can develop.

In addition to looking at systems with cooler G stars, the researchers
also looked at systems with K dwarf stars, which are somewhat cooler,
less massive and less luminous than our sun. K stars have the advantage
of long lifespans of 20 billion to 70 billion years. This would allow
orbiting planets to be older as well as giving life more time to advance
to the complexity currently found on Earth. However, to be habitable,
planets should not be so old that they have exhausted their geothermal
heat and lack protective geomagnetic fields. Earth is around 4.5 billion
years old, but the researchers argue that the sweet spot for life is a
planet that is between 5 billion to 8 billion years old.

Size and mass also matter. A planet that is 10% larger than the Earth
should have more habitable land. One that is about 1.5 times Earth's mass
would be expected to retain its interior heating through radioactive decay longer and would also have a stronger gravity to retain an atmosphere
over a longer time period.

Water is key to life and the authors argue that a little more of it would
help, especially in the form of moisture, clouds and humidity. A slightly overall warmer temperature, a mean surface temperature of about 5 degrees Celsius (or about 8 degrees Fahrenheit) greater than Earth, together with
the additional moisture, would be also better for life. This warmth and moisture preference is seen on Earth with the greater biodiversity in
tropical rain forests than in colder, drier areas.

Among the 24 top planet candidates none of them meet all the criteria for superhabitable planets, but one has four of the critical characteristics, making it possibly much more comfortable for life than our home planet.

"It's sometimes difficult to convey this principle of
superhabitable planets because we think we have the best planet,"
said Schulze-Makuch. "We have a great number of complex and diverse
lifeforms, and many that can survive in extreme environments. It is
good to have adaptable life, but that doesn't mean that we have the best
of everything."

========================================================================== Story Source: Materials provided by Washington_State_University. Original written by Sara Zaske. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Dirk Schulze-Makuch, Rene' Heller, Edward Guinan. In Search for
a Planet
Better than Earth: Top Contenders for a Superhabitable World.

Astrobiology, 2020; DOI: 10.1089/ast.2019.2161 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201005005919.htm

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