THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Founded January 1970
Julian date: 2457637.16
"Destined to explore 0.00000000000000000000000000004% of
the cosmos."
*THE DAILY ASTRONOMER*
*Monday, September 5, 2016 In Close Proximity to Proxima*
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STAR DOME ASTRONOMY
An introductory astronomy course begins
Tuesday, September 20, 2016
Six Tuesday evenings 7:00 - 9:00 p.m.
Open to all!
Call 207-780-4249 or consult our web-site
www.usm.maine.edu/planet for more information
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When beholding the faintly luminous Milky Way that traverses tonight's
evening sky from northeast to southwest, one should know that innumerable
undiscovered worlds lurk within that vast star field. As of this
moment, astronomers have confirmed the discovery of 3,375 exo-planets, or
planets bound to other star systems. This number will likely increase
soon, perhaps even by the time you actually receive this article. Based
on these discoveries, astronomers estimate that our galaxy's planet
population could easily exceed its stellar population of at least 250
billion. These exo planet detections have profoundly altered our
perception of the galaxy over the last generation, considering that only
twenty five years ago we knew of no planets outside our own solar
system.* The "whirlpool of stars" has been transfigured into an island
universe abundant in planetary systems.
As astronomers scan the skies for other worlds, they all share one ardent
wish: to detect another "Earth," a life-harboring world beyond our solar
system. Although our exo-planet catalogue is expanding almost by the
day, our knowledge of alien races -if they exist- is nil. Discovering
life elsewhere could exponentially expand our knowledge of life in
general, just as the exo planet detections have greatly augmented our
knowledge of solar systems. The problem is where to search for them and
how.
Based on our understanding of Earth life, astronomers believe that a
life-harboring planet must exist within its parent star's habitable zone: a
region where temperatures would permit life to survive. Life wouldn't
thrive on a planet that is either too close or too far away from its
central energy source. For this reason, habitable zones are often known as
"Goldilocks regions," neither too hot nor too cold. Finding a world
within such an orbit would not guarantee that it is life bearing. After
all, Venus and Mars are technically within the Sun's habitable zone, but
are both barren of life.
Astronomers have found such "habitable zone" planets before. In fact, they
have cataloged about 43 habitable zone planets, both "terran" (those with
masses between 0.5 - 5 times that of Earth) and "superterran" (those with
masses between 5 - 10 times that of Earth.) In August 2016, the European
Southern Observatory has added a 44th: Proxima b, a Earth-like planet in
orbit around Proxima Centauri, the red dwarf member of the ternary star
system Alpha Centauri. At a distance of 4.2 light years, Proxima Centauri
is the closest star to our solar system. Consequently, we can also now
say that Proxima b is the closest exo planet to us. Wonderfully, this
planet moves within Proxima Centauri's habitable zone and might contain
life within our own galactic neighborhood. Then, again, it might not.
Through the radial velocity method, which involves measuring how a star's
spectrum shifts relative to Earth (see today's "Catacombs of Infinite
Knowledge"), a research team headed by Guillem Anglada-Escude of Queen
Mary University of London determined that Proxima b's mean distance from
its star is 4.5 million miles and it completes one revolution every 11.1
Earth days. For comparison, Mercury's mean distance from the Sun is 36
million miles and its year is 88 Earth days. A planet would have to be so
close to Proxima Centauri to be within the star's habitable zone because
the star is only 0.17% as luminous as the Sun.
[image: cid:image003.jpg@01D206A3.A54DA210]
*An artistic depiction of Proxima Centauri (background) and *
*Proxima Centauri b (foreground). Proxima Centauri b is the closest*
*known exoplanet to our solar system. This planet is both slightly*
*more massive than Earth and orbits within its parent star's habitable
zone.*
*For these reasons, this planet might support life. Image: ESO*
The planet is also a Terran world, meaning that its mass within the range
of Terran planets (0.5 - 5.0 times Earth's mass.) At this point, the
research team can only estimate that the planet is about 1.28 times as
massive as Earth. In order to precisely calculate this mass, they need
to know the planet's inclination, or angle relative to us. They need to
know this inclination because they are measuring how much a star moves due
to its planet's gravitational influence. The more inclined a planet is
relative to us, the more massive it would have to be to induce the measured
wobble. The astronomers know the planet slightly more massive than Earth
and would also be terrestrial, or solid and rocky.
The problem, however, is with the planet's close proximity to Proxima
Centauri. Even though Proxima is a low luminosity red dwarf, it still
generates copious radiation. Although it would still appear
twilight-dim on Proxima b, it would still be bombarded with 400 times the
x-ray radiation that Earth receives. Unless Proxima b is enveloped in a
protective atmosphere similar to the one around Earth, its surface will be
bombarded by an ceaseless onslaught of high energy x-rays. Such
conditions would prove quite inhospitable.
However, we know now that at least one planet revolves around Proxima
Centauri, the closest star to the Sun. We know that it is an Earth-like
planet traveling with its parent star's habitable zone. We don't know if
it harbors life or even has the potential to do so. Many research teams
will definitely focus on Proxima b in the near future in an attempt to find
telltale signs of life, such as molecular oxygen, methane, and other
metabolic by products in its atmosphere. How lovely -and perhaps a
bit disquieting- to suddenly realize that our closest neighbors are far
closer than we thought they would be.
*The first confirmed discovery of exo-planets was announced in 1992, when
two planets were detected around the pulsar PSR B1257 +12 by the
astronomers Aleksander Wolszczan and Dale Frail. However, some science
historians date the first exo-planet discovery back to 1988, when a team of
Canadian astronomers lead by Bruce Campbell,** announced the detection of a
planet around Gamma Cephei. This discovery was not immediately
confirmed. In fact, the research team, itself, withdrew the claim in 1994,
citing insufficient data collection. However, in 2002, the discovery of a
planet around Gamma Cephei was finally confirmed.
**NO, not THAT Bruce Campbell!
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*FROM THE CATACOMBS OF INFINITE KNOWLEDGE: *What does 'spectrum shift"
mean?
Let's start by dividing light into its component colors: the "rainbow" of
red, orange, yellow, green, blue, indigo, violet. If the light passes
through nothing, then one could observe all these colors. However, if
the light passes through a material before it is split into its component
colors, one would observe a series of dark lines within the spectrum.
Atoms within the material will absorb light photons at specific
wavelengths. Each wavelength corresponds to a different color. For
instance, the wavelength of 445 nm (nanometers) is within the indigo part
of the spectrum. If atoms within the traversed medium absorb photons of
this wavelength, a dark line will appear in the indigo region.
[image: cid:image003.jpg@01D206B7.18275B60]
If the light source remains at rest, the dark lines will maintain their
positions. However, if the light source moves toward or away from an
observer, the lines will shift along the spectrum. This shift occurs
because the waves will either become elongated if the source moves away or
will become compressed if the light source approaches. We refer to these
wave changes as the "Doppler shift." If the waves are elongated,
they are 'red shifted," as the red part of the spectrum consists of longer
waves than the blue region. Conversely, if the waves are compressed, they
are 'blue shifted." When a planet tugs on a star toward Earth, the
star's spectrum is blue shifted. If the planet tugs on the star from the
other side of the star, the latter's light is red shifted. Many exo
planets are detected through the radial velocity method that measures the
periodic red and blue shifting that these planets induce on their parent
stars.
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