THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2459243.18
2020-2021: LXXIX
THE DAILY ASTRONOMER
Thursday, January 28, 2021
Exploratorium XIV: Runaway World
Location
300,000 light years outside the Andromeda Galaxy
Time
Christmas 2021
Christmas 2021
Feel that? Rock solid surface. Actually, I would say lead solid. Unfortunately, we can barely see anything. At this location, even starlight is largely absent. A handful of faint stars are scattered across this pitch black sky. The illumination they impart onto us is negligible.
The temperature? Well below -200 from pole to pole. The atmosphere that once enveloped this world has long since solidified and settled onto the surface. Oceans? Well, we're strolling across one of them. Below our feet is a column of super cold ice 3.7 miles thick. Although the deep interior retains residual heat from radioactive activity, it is too deeply embedded to affect the oceans. Water hasn't flowed here for millions of years. Everything is frozen solid and will remain that way for hundreds of millions of more years, if not much longer. You see, we're standing on a runaway world, a planet careening through the unfathomably vast gulfs of intergalactic space.
We came here on what is now Christmas morning 2021. That seemed appropriate because on Earth many people are celebrating both Christmas and winter's beginning. Here, on this barren frigid, dark, lifeless planet, the concept of seasons is meaningless. Also nonsensical are concepts of day and night. Yes, ths planet still rotates and has done so since its formation, but it doesn't turn toward any star's warming fires. We would only know of this rotation were we to remain here for 31 hours, During that time, we'd notice a fuzzy light patch slowly rise and a few hours later attain its maximum altitude and then a while later set. That patch is the Andromeda Galaxy, the grand spiral galaxy from which this planet was expelled so long ago when Andromeda devoured a minor satellite galaxy. The resultant dynamics and close stellar encounters dislodged many stars and their attendant worlds and cast them into the wild black yonder.
This sad, nameless world that hasn't welcomed any tourists before us since time immemorial would have fared much better had it remained gravitationally bound with its parent star. Had it done so, that star would have bestowed copious amounts of heat energy onto it and kept the land warm, the waters in liquid form and the life forms would have thrived. Though winters might have proven to be harsh, they would have also been finite in duration. Instead, we're walking across the planet's deepest sea in an eternal winter. In fact, the planet might have been better off had it remained within the Andromeda Galaxy where it might have been captured by a star. Now, well, the chances are extremely remote. The probability of a planet encountering a star out here is about equal to the chance of two darts being randomly tossed in North America and colliding tip to tip.
Why visit such an inhospitable world so far from home? Well, it gives us an opportunity to discuss the concept of renegade or runaway worlds. Astronomers believe that these planets might well number in the millions or billions through the Universe. Not only do large galaxies devour smaller ones, but planets and other bodies are often expelled from solar systems as they form. Consequently, both interstellar and intergalactic space could well be littered with these unattached worlds.
Apart from these imaginary wanderings, how could humans actually find any of these Runaway or Rogue Planets? Some astronomers such as Dr. Takahiro Sumi at the University of Osaka have used microlensing observations to detect a few rogue planets without any associated stars. Even relatively small bodies such as planets can distort more distant starlight by sending that light gravitationally. In 2020, microlensing enabled astronomers to detect their first Earth-sized Rogue planet, one named OGLE-2016-BLG-1928.
In 2025, the Nancy Grace Roman Telescope -seen below- is scheduled to launch. Part of this infrared telescope's aim is to image exo-planets and search for runaway planets within the galaxy. Those outside of galaxies are much more difficult to find.
In 2025, the Nancy Grace Roman Telescope -seen below- is scheduled to launch. Part of this infrared telescope's aim is to image exo-planets and search for runaway planets within the galaxy. Those outside of galaxies are much more difficult to find.
So, Merry Christmas 2021 to those on Earth. We few standing here on his world between galaxies are loitering on a place bereft of life, sound, light or seasons. If nothing else, spending time here will renew our appreciation for the Sun, even though, in winter, it serves as little more than ornamentation.
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