After
napping for a little over two years, the European Space Agency’s Rosetta is
ready to stretch her…panels. On the 20th of January this year the
ESA held a competition to see who could issue the best wake-up call to the
hibernating spacecraft. While I don’t know who won I do know they are quite
lucky, as they win a free trip to Mission Control in Germany to see what
Rosetta discovers.
In
2008 it passed a comet while flying by Mars. While 2867 Šteins had been
discovered in 1969, this was the first time clear images of the comet were
transmitted and its massive 5.6 km size could be clearly determined. In 2010
she flew by another one, 21 Lutetia, once again transmitting crystal clear
images of an asteroid discovered in 1852. How was it discovered in 1852 with
the limited technology available you ask? Probably because it’s over 1,000 km
in diameter. That’s astronomically huge! (pun intended)
What
makes this spacecraft so unique an sets her apart from other satellites is that
Rosetta is the first one to be powered solely by solar technology! As it
hibernated during its orbit around the sun to gain momentum its instruments
were powered down in order to conserve energy. But while it was powered down it
was gaining energy from the sun by
gathering it on its massive solar arrays. Hopefully this will give Rosetta the
extra “umph!” she needs to survive her mission out in deep space where she will
only receive 4% of the sun’s power.
It’s
been awhile since we’ve flown out into the deep reaches of space here at To Infinity
And…In Theory. So let’s strap on our rocket boots, throw on some Elton John,
and climb aboard the red eye to see what Rosetta and her little buddy Philae
the Lander have in store for scientists at the ESA.
Comets, Asteroids,
and Meteoroids
Yay!
We get to start with terminology. I know what you’re saying, “my favorite…” but
it’s important to understand there are very important differences between
comets, asteroids, and meteoroids. The only reason I do this is because
technically these words aren’t really interchangeable like so many others in
Astronomy. There are a few key variances.
Let’s
start with a comet.
Quite
possibly one of the most well-known comets is Halley’s. It was discovered in
1531. Then discovered again in 1607…and again in 1682. It wasn’t until a man
named Edmond Halley dug through the various reports of these sightings that he
came to one very important conclusion. This comet was the same one. He also
predicted that it would come back in 1758. While he didn’t live long enough to
see that he was right, plenty of other astronomers did, which led to this comet
being named after him.
So
what makes a comet a comet? A comet is defined as a relatively small solar
system body that orbits the Sun. When close enough to the Sun they display a
visible coma (a fuzzy outline or atmosphere due to solar radiation) and
sometimes a tail. But what creates the tail on a comet?
As
it passes by the sun (which as we know is pretty darn warm…) it begins to burn
gases and ice off the surface of the orbiting rock. These superheated gases
trail behind the asteroid, sometimes miles long, as it rockets through space.
This is what turns the space rock from an asteroid into a comet.
Speaking
of asteroids, let’s talk about those next.
That’s
Ceres. I know, I know, you’ve seen Armageddon and you’re saying “woah dude,
that isn’t an asteroid, that’s totally a planet.” Well you’re half right. It
was discovered in 1801 by Sicilian astronomer Giuseppi Piazzi. Originally he
thought it was a comet but upon further observation it was determined that it
was indeed a planet. Well…a dwarf planet. (They prefer to be called “Little
Celestial People”) But seeing as it floats within the asteroid belt, it’s
earned its moniker as an asteroid.
Asteroids
are small solar system bodies that orbit the Sun. Made of rock and metal, they
can also contain organic compounds. Asteroids are similar to comets but do not
have a visible coma (fuzzy outline and tail) like comets do. It floats happily
between Mars and Jupiter and actually contains one third of the mass of the
entire asteroid belt. (Once again…huge) That’s not to say that if it broke
orbit and passed close enough to the sun it couldn’t develop a tail, after all,
the surface is believed to be made of dust and ice, perfect conditions to grow
a coma. However that scenario is quite unlikely considering it’s been content
with its lot in life to this point.
The
third space rock type we’re going to talk about now is the Meteoroid. This
particular floating stone actually has three forms like a Dragonball Z villain.
Meteoroids are the first stage, Meteors are the second, and Meteorites are the
last. We’ll break down all three in the next section.
A
meteoroid is a small rock or particle of debris in our solar system. They range
in size from dust to around 10 meters in diameter (larger objects are usually
referred to as asteroids). But don’t mistake their smaller diameters for cute
and cuddly. Once they enter the atmosphere of Earth they become known as a
Meteor. Most of the time they’ll burn up in orbit, but as the blast in Chelyabinsk,
Russia in February of last year showed us that’s not always the case.
Once
a Meteoroid enters our atmosphere and becomes a Meteor about to cause an
impending strike it is officially classified as a Meteorite. The effects of a
Meteorite impact can be devastating, equivalent to several nuclear megaton
blasts. (Time to call in Bruce Willis) That’s why NASA’s new Near Earth Object
monitoring program is so important so we are able to identify threats like this
long before they enter our atmosphere in the future so we don’t end up embedded
in the crust of the Earth next to the dinosaurs.
So
why am I telling you all this? Because the ESA is looking to land on a comet
and it’s important to know the extreme challenges they face in doing this.
Comets slingshot through the solar system gradually gaining speed as they play
off the gravitational forces of the bodies they orbit. Asteroids like Ceres are
essentially locked in orbit unless a huge impact was to send them rocketing out
of alignment. (Typically that’s how an asteroid becomes a comet or a meteoroid)
Next
we’ll talk about the challenges the ESA faces, how they intend to overcome
them, and what they expect to learn from this unique mission into the far reaches
of space. Let’s start with the biggest one of all, how exactly they intend to
make contact with this orbiting mass. The details are far more intricate than
you may think.
Space Darts
We’ve
all played darts, but space agencies around the world have adapted the game to
a whole new level. Think of it like this. When you look at a dart board you
select the spot you want to hit. You close one eye, pull your arm back, take a
couple practice swings and release it. If you’re experienced, nine times out of
ten you hit what you’re aiming at.
Now
imagine that dart board is several million miles away. It takes more than
closing one eye and a deep breath to hit what they’re aiming for. It takes a
series of complicated mathematical equations, physics, and a whole plethora of
very expensive technology. Luckily, the ESA has all three down to a…well…a
science.
When
Rosetta was initially conceptualized in 1993 they were aiming at a different
dartboard altogether. Comet 46 P/Wirtanen was caught in the crosshairs but due
to postponements and complications with the rocket Ariane 5 ECA they switched
it up. So in 2004, when Rosetta was launched its new target was designated 67
P/Churyumov-Gerasimenko.
But
in order for Rosetta to “dock” with this comet certain parameters needed to be
met at the outset. First and foremost speeds have to be matched. But 67
P/Churyumov-Gerasimenko has been orbiting for a long time. It’s had thousands upon
thousands of years to gather the speed it moves at. Unfortunately, we don’t
have thousands of years to follow it in orbit trying to play catch up. So how
are they going to dock with it?
Through
a process called a Gravity Assist Maneuver or Gravitational Slingshot. What it’s
doing is moving around the sun and using its gravitational mass in order to
gain momentum. The process can be used to accelerate or even decelerate
depending on the arc of the object in motion. During its approach vector it
makes a wide loop first, then, in order to garner further velocity, the orbit
gets smaller and smaller on each approach until finally it’s commanded to break
free toward its target.
Think
of it in terms of a tether ball. The ball tied to the end of the string in this
analogy would be Rosetta; the pole that the string is attached to is the sun.
When the ball is struck hard enough it makes a lazy, slow loop around the pole.
As the string gets shorter and shorter the speed at which the ball is moving begins
to increase until it reaches its terminal velocity. If the ball were to be
released from the string it would rocket off in the direction of its trajectory
until outside factors like gravity and resistance pulled it down.
However,
as we all should know, the voids of space have no gravity or atmosphere;
therefore there is no resistance to slow the object down until it enters the
gravity of another celestial body. Because of this the object maintains its
velocity and is able to quickly get up to the speed of its intended target. But
this is just the first problem the ESA has to overcome, the second one, believe
it or not, is far more difficult in
comparison to that.
The
gravity on 67 P/Churyumov-Gerasimenko is a million times less than that of
Earth’s. In other words, one wrong step and you’re floating off into deep
space. (Yikes!) This poses a huge obstacle to the European Space Agency in
getting Rosetta’s lander Philae to catch a piggyback ride through space.
With
the gravity being so low on the surface of this comet one misstep could destroy
over two decades of hard work and effort. Because of this Philae was outfitted
with some special equipment to help it “stick” to the comet. Two harpoons will
inject themselves into the surface to anchor it in place. Philae has also been
equipped with self-righting landing gear to make sure he doesn’t tip over and
once the feet make contact they will drill into the surface, further ensuring
this multi-million dollar piece of tech doesn’t just fling off into space.
Outfitted
with several different instruments including radio-spectrographs and
sub-surface drills to take samples of the rock to determine the composition,
this may be one of the most ambitious projects launched in recent years. But
what exactly are they intending to learn from this mission? Would you believe
me if I told you they’re looking to answer the question of where we came from?
I hope so, because it’s basically the goal here.
But
how exactly will some barren ice rock in space tell us where the complicated
diversity of life on our planet originated from. Glad you asked. Let’s briefly explore
that next in our final section today.
From Space Rocks to
Building Blocks
Comet’s,
Asteroid’s, and Meteoroids are all capable of containing a variety of
materials. Certain classes of the space rocks contain mostly metals, some have
been found to be highly dense carbon (diamonds), and some are even stranger
still, because they contain organic compounds. If you don’t know, we’re organic
compounds, and if you subscribe to the theory of evolution such as I do, then
you know we all evolved from single celled organisms that likely were transported
here by these tourists of the solar system.
Our
planet didn’t start out as a planet. It started out as superheated gasses that
formed into heavy elements. As gravity pulled those elements together it formed
a solid mass. That solid mass slowly became heavier and generated more gravity
and passing comets, asteroids, and meteoroids were pulled into its gravity.
That is how we ended up with such a diversity of elements on the planets in our
solar system…well, theoretically anyway.
But
if some of the bacteria and organic compounds hitching a ride on the backs of
these objects survived the entry into atmosphere that would certainly explain
how we got here. That’s why landing on this comet is so important. By studying
the subterranean composition of it and the formation of its coma as it passes
the sun it will give scientists a much clearer understanding of exactly how
comets play into the evolution of our solar system.
Philae
is expected to make its daring descent onto the surface of 67
P/Churyumov-Gerasimenko later this autumn. I’ll be following this mission
closely in the news and when new information develops I’ll be sure to write a
follow-up blog on Rosetta and Philae. Until then, good morning, good morrow,
and Godspeed Rosetta. I hope you enjoyed your nap, because now it’s time to get
down to business.
-
Ryan
Sanders
Thanks as always for reading and be sure
to share this on Twitter, Facebook and Reddit and EVERYWHERE ELSE! J
You guys and gals continue to make this one of the most enjoyable and ambitious
undertakings for me to write and I hope they are just as enjoyable for you to
read. Comments, questions, or corrections are always welcome so feel free to
post them below. For further reading you can follow-up on any of the links
listed below. Happy learning everyone!
