THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
(207) 780-4249      usm.maine.edu/planet
43.6667° N    70.2667° W
Founded January 1970
2022-2023: XLI
Sunrise: 6:37 a.m.
Sunset: 4:15 p.m.
Civil twilight ends: 4:46 p.m.
Sun's host constellation: Libra the Scales
Moon phase: Last Quarter
Moonrise: 11:17 p.m.
Moonset: 1:32 p.m. (11/17/2022)
Julian date: 2459900.21
"I went to the hardware store and bought some used paint. It was in the
shape of a house." -Steven Wright

THE DAILY ASTRONOMER
Wednesday, November 16, 2022
Orbital Pandoras

___________________________________
[image:
merlin_195254193_650a29e7-3d2c-4b62-9735-a9a1999d8fff-articleLarge.jpg]
THIS IS YOUR BRAIN ON ASTRONOMY.
ANY QUESTIONS?
Do you have questions about astronomy?  Please send them to the "Daily
Astronomer."  We promise to do our best to answer these questions in a
timely fashion.
_________________________________________

We return to Pandora's Jar today and find two questions pertaining to
Earth's orbit.  The first refers to the effect of other planets. The second
pertains to the possibility of moving Earth  away from the Sun before it
becomes too hot and bloated.


*DO PLANETS AFFECT EARTH'S ORBIT?  -F.N.*Scarcely at all. Theoretically,
every massive object exerts a gravitational influence on every other
massive object. The extent of that influence is proportional to the mass of
the object and inversely proportional to the square of the separation
distance between the objects. [Example: Double the distance between two
asteroids and the gravitational force between them reduces to a quarter of
its original amount.] We refer to this relation as Newton’s Universal Law
of Gravitation.

[The Universal Law of Gravitation equation. F = gravitational force; G =
gravitational constant 6.67 X 10^-11 m^3 kg^-1 s^-2; m1 = mass of one
object; m2 = mass of second object; r = separation distance. Included in
Newton’s Philosophiae Naturalis Principia Mathematica (Mathematical
Principles of Natural Philosophy) published in 1687.]

However, compared to the Sun, the masses of the planets are extremely small
and their distances -which are constantly changing- are vast. For instance,
the Sun is 1047 times more massive than Jupiter, the most massive planet.
(Also, Jupiter’s minimum distance from Earth approximately equals 366
million miles, compared to Earth’s average distance from the Sun of 93
million miles.) Even when closest, Jupiter’s gravitational force on Earth
is only 0.0062% that of the Sun’s. For comparison, the Moon’s force is 0.55%

That having been said, the perturbations induced on planetary orbits by
other planets are measurable. For instance, Brirtish astronomer John Couch
Adams (1819–1892) and French astronomer Urbain LeVerrier (1811–1877)
independently discovered Neptune in 1846 by observing the
then-unaccountable perturbations in the orbit of Uranus. They both
correctly concluded that a more distant planet was responsible for the
shifts.

So, the other planets do affect the orbit, albeit slightly.


*WOULD WE BE ABLE TO MOVE EARTH BEFORE THE SUN BECOMES A RED GIANT?   -
J.T.*

First, I should mention that we would need to “move” Earth prior to the
stage at which the Sun expands to the red giant stage. This transformation
is due to occur in 5–6 billion years, when the Sun exhausts its core
hydrogen reserves. However, the Sun’s luminosity (energy output per second)
is slowly increasing as a consequence of the thermonuclear core reactions.
Astronomers estimate that the Sun’s luminosity increases by 6% every
billion years. Consequently, Earth will be rendered uninhabitable in
approximately 1.1 billion years.


In order to keep Earth habitable, we’d have to move to the Sun within 1.1
billion years and continuously shift its position away from the Sun because
the habitable zone, the region in which temperatures are conducive to
life’s survival, would also expand away from it. By the time the Sun
becomes a red giant, the habitable zone will have extended all the way out
to the orbits of Jupiter and Saturn. (Jupiter’s average heliocentric
distance is 483 million miles; Saturn’s mean distance is 914 million
miles.) See graphic below.

The changing “Habitable Zone.” Earth is presently located within Earth’s
habitable zone, hence our continued existence on it. However, as the Sun’s
luminosity increases, this zone will expand away from the Sun. Earth will
be rendered uninhabitable in about 1.1 billion years. By the time the Sun
expands to the red giant stage, the habitable zone will be hundreds of
millions of miles farther away: in the region where Jupiter and Saturn
revolve around the Sun. Image: Astronomy Magazine

A few physicists have actually considered the possibility of shifting Earth
to protect it from the evolving Sun. One can well imagine that shifting
Earth safely constitutes one of the most challenging astro-engineering
problems. Perhaps the most feasible option discussed so far would be to
direct comets and asteroids with widths exceeding 100 kilometers around
Earth and then to either Jupiter or Saturn. The “pull” caused by these
repeated revolutions, though quite small, could cumulatively direct Earth
gradually but inexorably away from the Sun. Of course, this solution poses
many problems, namely, maintaining control of these bodies to ensure that
none of them eventually crashes onto Earth. Considering that the impact of
a 10-km wide asteroid ended the Cretaceous period, the consequences of a
100-km wide asteroid -taking into account the 1:10 ratio between the
impacting body’s diameter and that of the produced crater- could put an end
to Earth life itself.

Fortunately, we have plenty of time to contemplate the matter. That last
statement presumes that our species will even persist for 1.1 billion years
-4,400 times longer than the present duration of homo sapiens. If humans
are still extant by this time, presumably they would have devised a
solution to either shift Earth away from the Sun or to actually move to
another star system altogether. While the latter option would be the
logistically easier of the two, who knows what technology will develop in
the intervening time. After all, humans are known for their problem-solving
and, admittedly, problem-creating, capacities.



To subscribe or unsubscribe from the Daily Astronomer:
https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1