THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
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70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian date: 2458738.5
2019-2020: VIII
"I want to live in a society in which a chicken can cross the
road and not have its motives questioned."
-Seen on a bumper sticker
THE DAILY ASTRONOMER
Thursday, September 12, 2019
Water World
For the very first time, astronomers have found water an Earth-like
exo-planet! Moreover, this planet, K2-18b, is a "Super-Earth," an immense,
potentially rocky world revolving with its parent star's habitable zone.
It is, as Angelos Tsiaras, the University College London astronomer who
led the study that detected the world, described, "...the best
candidate for habitability we know right now."
This announcement has elicited glee from the astronomical community because
the principal aim of exoplanet seekers is to find a life-bearing world.
K2-18b is the first exo-planet known to have water vapor in its atmosphere
while being within the habitable zone, defined as the region in which
temperatures will allow for the presence of surface water. Of all the
exoplanets discovered so far (4,111 as of today), this planet shows the
most promise in actually harboring some form of life.
Astronomers do not yet have the capability of detecting water on an
exo-planet's surface. Instead, they analyze planet's reflected starlight
to detect water's spectral signature. Water, like other chemicals within
a planet's atmosphere, absorbs light at specific wavelengths. Astronomers
will know if water is present in the exo-planet's atmosphere if they
observe this spectral absorption sequence. The Hubble Space Telescope
captured this data from the planet as it moved in front of the star,
allowing the light to filter through the atmosphere.
One truly important issue remains unresolved: the amount of water present.
While spectral analysis can reveal water's presence, it cannot provide
information about the content. Current modeling places the percentage of
water in K2-18b's atmosphere between 0.01 - 50 percent. This planet might
harbor a trace amount of water or a high abundance. If the water level is
low, life probably won't exist on this planet. That statement is based
on our presumption that all life requires water: a presumption that might
prove quite mistaken.
It would be a lovely opportunity to gaze at the sky toward the direction of
K2-18 while contemplating the existence of extraterrestrial life. Of
course, the star is located within the Leo the Lion region, which is now
obscured by the Sun. However, one can still admire the sunset and
imagine that descending with it is a small space of sky in which life might
be evolving at this very minute. After all, at a distance of 111 light
years, K2-18b might be one of the closest of the life-bearing worlds to
Earth...perhaps only one of millions of such planets in our galaxy alone.
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