Psyche – The Mission to a Metal World – A Talk by Linda Elkins-Tanton
On Monday Oct 7, 2019, Dr. Linda
Elkins-Tanton (a.k.a. Lindy), project lead for the Psyche Asteroid Mission
planned by NASA did a presentation at the University of Alberta, concerning the
upcoming mission. It was well attended
and well received and quite fascinating.
Note that my blog on the talk is based primarily on notes that I took,
so between the difficulty of taking down notes quickly, and the difficulty of
reading my own handwriting, there may be some mistakes or omissions.
The Speaker
Dr. Elkins-Tanton is
a professor at Arizona State University, and director of the School of Earth
and Space Exploration at that university.
She is a geologist and an expert in planetary scientist and
evolution. She has also been a professor
at M.I.T. (her degrees in geology and geo-chemistry are from there), as well as
working at Brown and St. Mary’s College and worked in the private sector for a
number of years.
I might also add that she is an
excellent speaker who transmitted her enthusiasm and knowledge of these
subjects to the audience very well, and with an easy style and grace that helped us understand the sometimes difficult subject matter that underlies the
mission. She also did an excellent job
of explaining the details of the rather arduous job of persuading NASA to pick
one particular mission over the many others that are constantly being reviewed.
Getting Funding for the Mission and the Mission Schedule
Being chosen by NASA for a
mission, is a mission in itself, as Dr. Elkins-Tanton made clear. I have also heard this emphasized in other
NASA-project related talks, such as the New Horizons mission to Pluto. There is a lot of money and scientific
prestige at stake, and many projects compete to receive funding and other
forms of NASA support. In this case,
about 30 teams began the competition in 2011, and that was whittled down to 5
by 2015, which included the Psyche proposal.
At the final proposal competition,
the Psyche team had a very visually impressive “mission trailer” (basically a
short movie), as well as many eye-catching illustrations, by artist Peter Rubin,
who has done a great deal of work for very well-known movies and video games. He has a Canadian connection (possibly even
local via Electronic Arts), as his web-site states “I'm a US citizen married to
a Canadian; I live in Los Angeles and divide my time between there and the
Great White North.”
The trailer and other artwork is
pretty amazing, and no doubt helped to sway the NASA judges, though obviously
the scientific merit of the project had to be the primary consideration. Still, sizzle and steak generally work
together, in such matters, or it could be restated as “imagination and science”.
Note that the picture above
captures the period just after the asteroid (then planetesimal) Psyche has been
hit by another body, with the consequent melting and partial disaggregation, due
to the immense amount of kinetic energy that would result from the collision.
Along with the movie about the
collision which probably created Psyche, the NASA judges were provided with a “flip
book” based on the movie, so that they could quickly flip the pictures and “see”
the movie, just like people do when they are kids and get a flip book in a
cereal box. That’s because the video
couldn’t be included in the formal documents for the presentation, so the
flip-book was provided instead, to get around that restriction.
So, with the help of science and
art, the proposal won the big prize in 2016, which included funding to the tune
of $863 million (U.S.). I should also
note that this mission was funded under the “Discovery” class, which is a class
of missions below the “Flagship” class, which get higher funding and publicity –
these would generally be the “big” missions, such as Mars lander missions. The “New Horizons” class is on par with the Discovery
class, though the Pluto mission, which is probably the most famous New Horizons
mission, certainly got the public’s attention, very possibly equivalent to a
Flagship mission (or maybe that’s just me).
The Spacecraft and the Journey to Psyche
The spacecraft is now in the
building and design stage. The main
industry partner (an industry partner is a necessary condition for these
missions, as stipulated by NASA) is a corporation called Maxar Technology, via
the SSL (Space Systems Loral) company that they own. It also has a Canadian connection, formerly
being MDA, a Canadian satellite company.
The most interesting aspect of
this, is that the spacecraft will be using solar-electric propulsion for part
of the trip, which has been a specialty of this company, used to place satellites
in high Earth orbit. The other
interesting aspect, is that this allowed the project to come in at a much lower
price than NASA expected, about $100 million less.
The spacecraft will by about 3
meters by 2 meters, or roughly 10 feet
by 6.5 feet. It will be fitted with a
number of instruments:
- Gamma-ray and neutron spectrometers, to analyse the surface composition (these would be emitted from cosmic ray collisions on the surface, which would be intercepted and analysed by the spacecraft, while orbiting the asteroid).
- Cameras to photograph the surface of Psyche.
- Magnetometers to measure the magnetic field around the asteroid.
- Some ten solar panels, for electricity, which will be equivalent in area to a tennis court,
- An X-band antenna for communication. There is also a DSOC, explained below, though radio communication will still be needed.
- DSOC, a laser-based technique for sending information back to Earth, which will utilize super-conducting nano-wires. This will be a test case for the technology, its first major use by NASA. It will permit far greater bandwidth than conventional radio transmission, though it has the disadvantage of not penetrating clouds. During cloudy conditions, the data will be stored by Earth-based satellites and relayed to Earth once the weather clears.
- An SPT ion thruster, which needs a big box of Xenon for fuel (reaction mass). The xenon will be ionized, and then accelerated by an electric field, resulting in it shooting out of the thruster to provide propulsion via the usual conservation of momentum principle utilized by chemical rockets. Basically, a lot of the spacecraft will be a big 960 kilogram box of xenon fuel.
It is expected to be launched in
2022 by either an Atlas 4 or Falcon Heavy rocket and will reach Psyche in
2026. The mission plan includes a gravity
assist via a Mars flyby in 2023, to help it on its way to Psyche. Psyche is in the Asteroid Belt, between Mars
and Jupiter, a long way out, so the mission length will total about 2.904
billion kilometers.
The spacecraft mission is planned
to include 4 orbits of the asteroid, with each orbit getting the craft closer
and closer to Psyche. There is some
uncertainty about this, though, as we don’t yet know the shape of the gravity
field around Psyche, which will affect the details of the orbits. This was essentially the case for the Rosetta
mission to a comet as well. With small
bodies, we just can’t be sure what they are like until we get pretty close to
them.
In any case, the orbits should
last for about a year, at which time the orbiter will become a “lander”, though
it won’t be a soft landing (i.e. it will be crashed into the surface).
Another notable feature of the
mission is that results will be made public, via the internet, within 30
minutes of the signals being received.
Though, if there are any freaky artificial monoliths there, I doubt they
will keep that promise. :)😊
The Science of the Asteroid Psyche – The Mission to a Metal World
Spacecraft missions are exciting,
but they need a purpose, and that purpose is science and discovery. And the mission to Psyche promises to deliver
a lot of interesting science.
First off, will this really be a
metal world? And what does that mean,
anyway?
We can’t really be sure what we will
find until we get there, but there is good reason to believe that Psyche has
major metal content. At one time, it was
thought to be up to 90% metal, but some recent observations imply that it might
be more like 30-60% metal.
The reason that Psyche is
interesting, is its unusual apparent density, which seems to be about 4.0, in
terms of specific gravity (grams per cubic centimeter). Other asteroids are considerably less dense
than that, often between 2 and 3. For
comparison, Earth’s density is about 5.5.
The presence of high metal content
(which is more dense than rock) would account for Psyche’s high density. The metals involved are expected to be iron
and nickel, as those are the main constituents of the deep interior of the
Earth, and iron-nickel meteorites have been found on Earth, which establishes
that such material exists in space as well.
There are some uncertainties in
the measure, however. Estimating density
requires knowing the volume of the body and the mass contained in the body. For
volume, we need to know its size and shape, but our best Hubble photos of
Psyche only span two pixels, so we can’t be all that sure about its dimensions. That said, with the Hubble photos, as well as
radar signals, it is thought that Psyche is probably somewhat oblong and is about
200 km in radius.
As for its mass, that is inferred
from its gravitational interactions with nearby bodies, which makes that a
tricky estimate too. However, our best estimates
still say that Psyche is substantially heavier than normal and probably
accounts for about one percent of the total mass of the Asteroid Belt.
So, how did this unusual body
form? The basic hypothesis is that it
was the result of a collision (or maybe several) between some large bodies in
the early development of the solar system, probably within the first 1.5
million years. Theory says that larger
bodies (such as planets) were formed by multiple collisions and agglomerations
over several million years, so collisions are assumed to be rather frequent in
the early stages of a solar systems origin.
In Psyche’s case, it is thought
that a “hit and run” collision occurred, with the core of a protoplanetary
object. These objects would have been
hot, because of radioactive decay of hot, short-lived radioactive elements that
would have been abundant early in the solar system’s history. Those elements would have been made during
the supernova of a previously existing large star, which created the seed
matter for the sun and planets, and would have “burned out” by now, 4.5 billion
years later.
So, two hot, possibly molten
bodies collided, with one glancing off the other and ending up who-knows-where,
while the other stayed in the Asteroid Belt and became Psyche. It is thought that the molten metal of the
collision would re-coalesce and freeze in space, creating the unusual
metal-heavy object Psyche.
There are some
interesting consequences of this theory.
One is that Psyche might look pretty weird, with unusual topography:
·
There may be large and sharp “contract scarps”
caused by shrinking as the metal cooled (iron-nickel would be about 7% more
dense as it freezes than when it is molten).
·
There could also be sulphur-rich volcanoes, as
sulphur would be excluded from the melt and separate out, rising to the surface,
creating these features.
·
The craters caused by later collisions could be
quite strange looking. Lab experiments on
high speed collisions with metal matrixes indicate that the crater edges don’t
fall back the way that they do on Earth or the moon, but could become “frozen”
before the rebound that craters undergo in rocky environments.
There is also the possibility that Psyche will have
an unusual magnetic field. Assuming that
the body had a dynamo (rotating iron-nickel core) in its early stages, that
could be “frozen in” as Psyche cooled and might still be there, rather like a
powerful bar magnet. If so, one wonders
whether it might have some interesting interactions with the solar wind.
All of
this is conjecture, though. So far, we
have some long-distance measurements, lots of theory, some relevant lab
experiments and many Monte Carlo computer simulations. The proof of the pudding will be in the
eating, or in this case, the close-in views and measurements that we should see
in about 6 or 7 years time, assuming that all goes well.
Now that you have read of some cutting edge science, you
should consider reading some Science Fiction.
How about a short story, set in the Arctic, with some alien and/or
paranormal aspects. Only 99 cents on
Amazon.
The Magnetic Anomaly: A Science Fiction Story
“A geophysical crew went into the Canadian north. There were
some regrettable accidents among a few ex-military who had become geophysical
contractors after their service in the forces. A young man and young woman went
temporarily mad from the stress of seeing that. They imagined things, terrible
things. But both are known to have vivid imaginations; we have childhood
records to verify that. It was all very sad. That’s the official story.”
Amazon U.S.: https://www.amazon.com/dp/B0176H22B4
Amazon U.K. https://www.amazon.co.uk/dp/B0176H22B4
Amazon Canada. https://www.amazon.ca/dp/B0176H22B4
“The Zoo Hypothesis”, an Alien Invasion Story
Here’s a story giving a
possible scenario for the so-called Zoo Hypothesis, known in Star Trek lore as
the Prime Directive. It’s an explanation
sometimes given to account for a mystery in the Search for Intelligent Life,
known as The Great Silence, or Fermi’s Paradox.Basically, Enrico Fermi argued (quite convincingly, to many observers), that there had been ample time for an alien intelligence to colonize the galaxy since its formation, so where are they? The Zoo Hypotheses says that they are out there, but have cordoned off the Earth from contact, until we are sufficiently evolved or culturally advanced to handle the impact of alien contact.
This story takes a humorous tongue in cheek approach to that explanation. It also features dogs and sly references to Star Trek. Talk about man’s Best Friend.
Amazon U.S.: https://www.amazon.com/dp/B076RR1PGD
Amazon U.K.: https://www.amazon.co.uk/dp/B076RR1PGD
Amazon Canada: https://www.amazon.ca/dp/B076RR1PGD
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