From its history, to its potential for being a base for humanity, and more!
Join as us as we explore Phobos, Mars' Moon!
7.
History Of Phobos Phobos was discovered by astronomer Asaph
Hall on 18 August 1877, at the United States Naval Observatory in Washington, D.C., at
about 09:14 Greenwich Mean Time (contemporary sources, using the pre-1925 astronomical convention
that began the day at noon, give the time of discovery as 17 August at 16:06 Washington
mean time, meaning 18 August 04:06 in the modern convention).
Hall had discovered Deimos, Mars's other moon, a few days earlier on 12 August 1877 at about
07:48 UTC.
The names, originally spelled Phobus and Deimus respectively, were suggested by Henry Madan
(1838–1901), science master at Eton College, based on Greek mythology, in which Phobos
is a companion to the god Ares.
Speculation about the existence of the moons of Mars had begun when the moons of Jupiter
were discovered.
When Galileo Galilei, as a hidden report about him having observed two bumps on the sides
of Saturn (later discovered to be its rings).
Hall recorded his discovery of Phobos in his notebook as follows:
"I repeated the examination in the early part of the night of 11th [August 1877], and again
found nothing, but trying again some hours later I found a faint object on the following
side and a little north of the planet.
I had barely time to secure an observation of its position when fog from the River stopped
the work.
This was at half past two o'clock on the night of the 11th.
Cloudy weather intervened for several days.
On 15 August the weather looking more promising, I slept at the Observatory.
The sky cleared off with a thunderstorm at 11 o'clock and the search was resumed.
The atmosphere however was in a very bad condition and Mars was so blazing and unsteady that
nothing could be seen of the object, which we now know was at that time so near the planet
as to be invisible.
On 16 August the object was found again on the following side of the planet, and the
observations of that night showed that it was moving with the planet, and if a satellite,
was near one of its elongations.
Until this time I had said nothing to anyone at the Observatory of my search for a satellite
of Mars, but on leaving the observatory after these observations of the 16th, at about three
o'clock in the morning, I told my assistant, George Anderson, to whom I had shown the object,
that I thought I had discovered a satellite of Mars.
I told him also to keep quiet as I did not wish anything said until the matter was beyond
doubt.
He said nothing, but the thing was too good to keep and I let it out myself.
On 17 August between one and two o'clock, while I was reducing my observations, Professor
Newcomb came into my room to eat his lunch and I showed him my measures of the faint
object near Mars which proved that it was moving with the planet.
On 17 August while waiting and watching for the outer moon, the inner one was discovered.
The observations of the 17th and 18th put beyond doubt the character of these objects
and the discovery was publicly announced by Admiral Rodgers."
6.
Orbits and Rotations The orbital motion of Phobos has been intensively
studied, making it "the best studied natural satellite in the Solar System" in terms of
orbits completed.
Its close orbit around Mars produces some unusual effects.
With an altitude of 5,989 km (3,721 mi), Phobos orbits Mars below the synchronous orbit radius,
meaning that it moves around Mars faster than Mars itself rotates.
Therefore, from the point of view of an observer on the surface of Mars, it rises in the west,
moves comparatively rapidly across the sky (in 4 h 15 min or less) and sets in the east,
approximately twice each Martian day (every 11 h 6 min).
Because it is close to the surface and in an equatorial orbit, it cannot be seen above
the horizon from latitudes greater than 70.4°.
Its orbit is so low that its angular diameter, as seen by an observer on Mars, varies visibly
with its position in the sky.
Seen at the horizon, Phobos is about 0.14° wide; at zenith it is 0.20°, one-third as
wide as the full Moon as seen from Earth.
By comparison, the Sun has an apparent size of about 0.35° in the Martian sky.
Phobos's phases, inasmuch as they can be observed from Mars, take 0.3191 days (Phobos's synodic
period) to run their course, a mere 13 seconds longer than Phobos's sidereal period.
As seen from Phobos, Mars would appear 6,400 times larger and 2,500 times brighter than
the full Moon appears from Earth, taking up a quarter of the width of a celestial hemisphere.
An observer situated on the Martian surface, in a position to observe Phobos, would see
regular transits of Phobos across the Sun.
Several of these transits have been photographed by the Mars Rover Opportunity.
During the transits, Phobos's shadow is cast on the surface of Mars; an event which has
been photographed by several spacecraft.
Phobos is not large enough to cover the Sun's disk, and so cannot cause a total eclipse.
5.
Surface Phobos and Deimos appear to be composed of
C-type rock, similar to blackish carbonaceous chondrite asteroids.
Observations by Mars Global Surveyor indicate that the surface of this small body has been
pounded into powder by eons of meteoroid impacts, some of which started landslides that left
dark trails marking the steep slopes of giant craters.
Measurements of the day and night sides of Phobos show such extreme temperature variations
that the sunlit side of the moon rivals a pleasant winter day in Chicago, while only
a few kilometers away, on the dark side of the moon, the climate is more harsh than a
night in Antarctica.
High temperatures for Phobos were measured at 25 degrees Fahrenheit (-4 degrees Celsius)
and lows at -170 degrees Fahrenheit (-112 degrees Celsius).
This intense heat loss is likely a result of the fine dust on Phobos' surface, which
is unable to retain heat.
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4.
Controversial Origin The origin of the Martian moons is still controversial,
which is interesting given how long we've been studying them.
Phobos and Deimos both have much in common in regards to their composition and even their
shape and size in certain areas.
Based on their similarity, one hypothesis is that both moons may be captured main-belt
asteroids.
Both moons have very circular orbits which lie almost exactly in Mars's equatorial plane,
and hence a capture origin requires a mechanism for circularizing the initially highly eccentric
orbit, and adjusting its inclination into the equatorial plane, most probably by a combination
of atmospheric drag and tidal forces, although it is not clear that sufficient time is available
for this to occur for Deimos.
Capture also requires dissipation of energy.
The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric
braking.
Geoffrey A. Landis has pointed out that the capture could have occurred if the original
body was a binary asteroid that separated under tidal forces.
Phobos could be a second-generation Solar System object that coalesced in orbit after
Mars formed, rather than forming concurrently out of the same birth cloud as Mars.
Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps
ejected into orbit around it by a collision with a large planetesimal.
The high porosity of the interior of Phobos is inconsistent with an asteroidal origin.
Observations of Phobos in the thermal infrared suggest a composition containing mainly phyllosilicates,
which are well known from the surface of Mars.
The spectra are distinct from those of all classes of chondrite meteorites, again pointing
away from an asteroidal origin.
Both sets of findings support an origin of Phobos from material ejected by an impact
on Mars that reaccreted in Martian orbit, similar to the prevailing theory for the origin
of Earth's moon.
The irony here is that it's hard to tell which of these theories is true.
Especially since we're still evaluating the origins of Mars itself.
Only through various tests on both the planet and the moon/moons can we likely find the
true of what is going on.
3.
Could Phobos Be Hollow?
If it's not clear by now, Phobos is a very unique moon compared to many of the others
within our solar system.
But one man has noted that there may be a just as unique way of explaining it all.
Mainly, this person believes that Phobos...could be hollow.
Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular
acceleration of Phobos's orbital motion, suggested a "thin sheet metal" structure for Phobos,
a suggestion which led to speculations that Phobos was of artificial origin.
Shklovsky based his analysis on estimates of the upper Martian atmosphere's density,
and deduced that for the weak braking effect to be able to account for the secular acceleration,
Phobos had to be very light—one calculation yielded a hollow iron sphere 16 kilometers
(9.9 mi) across but less than 6 cm thick.
In a February 1960 letter to the journal Astronautics, Fred Singer, then science advisor to U.S.
President Dwight D. Eisenhower, said of Shklovsky's theory:
"If the satellite is indeed spiraling inward as deduced from astronomical observation,
then there is little alternative to the hypothesis that it is hollow and therefore Martian made.
The big 'if' lies in the astronomical observations; they may well be in error.
Since they are based on several independent sets of measurements taken decades apart by
different observers with different instruments, systematic errors may have influenced them."
These errors were indeed found, and later observations and investigations revealed that
Phobos is a kind of "rubble pile" moon.
In addition, images obtained by the Viking probes in the 1970s clearly showed a natural
object, not an artificial one.
Nevertheless, mapping by the Mars Express probe and subsequent volume calculations do
suggest the presence of voids and indicate that it is not a solid chunk of rock but a
porous body.
So while it was a curious theory, and one that would have rewritten history, it was
not one that was proven to be true by any metric.
2.
Could Phobos Be Destroyed Via Natural Patterns?
Tidal deceleration is gradually decreasing the orbital radius of Phobos by two meters
every one hundred years.
Scientists estimate that Phobos will be destroyed in approximately 30–50 million years, with
one study's estimate being about 43 million years.
Phobos' grooves were long thought to be fractures caused by the impact that formed the Stickney
crater.
Other modelling suggested since the 1970s support the idea that the grooves are more
like "stretch marks" that occur when Phobos gets deformed by tidal forces, but in 2015
when the tidal forces were calculated and used in a new model, the stresses were too
weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded
by a layer of powdery regolith about 100 m (330 ft) thick.
Stress fractures calculated for this model line up with the grooves on Phobos.
The model is supported with the discovery that some of the grooves are younger than
others, implying that the process that produces the grooves is ongoing.
Given Phobos's irregular shape and assuming that it is a pile of rubble (specifically
a Mohr–Coulomb body), it will eventually break up when it reaches approximately 2.1
Mars radii.
When Phobos is eventually torn apart by tidal forces, a fraction of the debris will likely
form a planetary ring around Mars, which may last from one million to one hundred million
years.
A very interesting end for a very interesting for a very interesting moon.
1.
Colony On Phobos?
As you all likely know, both NASA and SpaceX are preparing themselves for a mission of
grand importance: They're going to try and colonize Mars.
This mission will take many years to fully complete, and launch for the first part will
be in the next few years.
But, many are already planning for what is to come after we truly make contact on Mars.
Mainly, once the "main colony" is setup...we'll immediately start expanding.
Now the initial thought is to go to another planet to colonize, or a moon of a planet
beyond Mars.
But many are thinking that Mars could be a perfect launchpoint for a set of colonies.
Mainly, have a main one on Mars to start, and then have waypoint stations on Phobos
and Deimos.
But why do that?
Because it would allow for easier transition both in and out of Mars's atmosphere (which
is thin but still there) and its gravity pull.
There are some who even speculate that a certain kind of perpetual motion machine can be put
on the moons to help launch ships into the asteroid belt area that separates Mars and
Jupiter and thus make it easier to get into the back half of the solar system.
Plus, having bases on the moons could allow for travel between Earth and Mars and beyond,
as well as potentially setting up mining stations for going into the asteroid belt and seeking
out materials there.
Granted, this is a lot of theories at the current moment.
However, there are plans in motion that could make this happen.
The only question is how soon this could potentially happen, which obviously will be decided based
on the main Mars mission.
Thanks for watching everyone!
What did you think of this look at Phobos?
Do you think that it's as interesting as the astronauts who have studied it think it is?
Do you think that in our attempts to colonize Mars we'll colonize Phobos too?
Let us know in the comments below, be sure to subscribe, and I'll see you next time on
the channel!