A final salute to Starman, the world's loneliest astronaut. It will be the
Moon next Aug. 14 that will show us the exact point in the sky to which to send our thoughts
Hey guys, how are you doing with the night sky?
Do you know how to recognize stars and constellations?
Don't worry though... If you really have no idea how to orient yourself in the sky,
just take a look at this map, which we will propose again at the end of this talk.
And if some of you are wondering why you should do this, the reason is:
in this way you will be able to answer a question that certainly has often crossed
your mind of space enthusiasts... that is: where is Starman now?
You know exactly what I'm talking about... not the alien visitor played by Jeff Bridges in the movie
of the same name, but the silent astronaut who has been piloting a red Tesla Roadster car around the
Sun for more than three and a half years. Do you remember? Given the risk of launch
failure (it was assumed 50% chance that the rocket exploded on the ramp, as happened in the previous
test), to test what at the time was supposed to be the most powerful rocket in the world, the
Falcon Heavy, SpaceX needed a dummy load, that is of no importance in scientific and economic terms.
Elon Musk, the patron of both SpaceX and Tesla, therefore chose his personal
Roadster instead of a simple ballast, putting at the wheel a dummy wearing the prototype of
the next-generation spacesuit. The same one that we have then really seen in the Crew
Dragon astronauts heading to the Space Station. Musk himself had declared that given the high
probability of launch failure he would not have chosen as payload anything too sentimental or
irretrievable. Adding that usually for demonstration missions like that they usually
choose payloads as trivial as concrete blocks, and that he wanted to opt for something more
frivolous "because even the ridiculous things are important".
Within the first five hours of launch, three cameras mounted on a stand showed the Tesla
Roadster and its passenger Starman, with his elbow set out the window, hurtling through Space with
Earth in the background. The streaming lasted as long as the Tesla's batteries lasted, then Starman
disappeared forever from our visual horizon, piloting alone along a road that some sources
said would take him to the Main Asteroid Belt. In fact, from a review of the calculations of
the orbital parameters released by the Jet Propulsion Laboratory,
it seems now established that the Tesla has not had sufficient thrust to reach that destination,
and that it is traveling along an orbit that at aphelion takes it just beyond the Martian orbit.
The Roadster, in fact, is now in a heliocentric orbit that crosses the orbit of Mars and reaches
a distance of 1.66 Astronomical Unit from the Sun, equal to about 250 million kilometers.
With a slight inclination with respect to the orbital plane of Mars, so it will never be
possible for the Tesla to impact the planet or be captured by its gravitational field.
And anyway, even if the rocket had by chance taken a transfer orbit to Mars, the car could
not have been put into orbit around Mars, because the second stage of the rocket that carries it
is not equipped with propellant, nor the necessary maneuvering and communication capabilities.
The flight organized by SpaceX was simply intended to demonstrate that Falcon Heavy
is capable of launching significant payloads to Mars on potential future missions.
It has also been calculated that over a very long period of 3 million years the probability of Tesla
colliding with Earth is no more than 6%. But the question at this point is,
will Starman's quiet cosmic navigation last
that long? Elon Musk stated that car and pilot could stay in space for billions of years.
And that in this sense they could become one of the longest-lived records of human existence.
The problem is that even in the vacuum of space, alas, we age. And not necessarily well.
According to some material experts, in fact, Starman's youth will last very little.
Outside the Earth's atmosphere, the silent pilot and his car are in fact constantly
bombarded by cosmic rays and solar wind. Most of the materials in the Tesla and Starman's spacesuit
(and presumably the dummy itself) are organic polymers: plastics and rubber, to be precise.
Whose chemical bonds are not made to withstand a continuous bombardment of high-energy particles.
"Hey, guys, just a moment before we continue... BE sure to join the Insane
Curiosity Channel... Click on the bell, you will help us to make products of ever-higher quality!"
You know when a rubber band or plastic item left in the sun for months or years becomes brittle,
discolored, and cracks? About the same thing, but more violent. According to chemist William
Carroll, of Indiana University, in a year Tesla's organic materials will be shattered.
Carbon fiber will last a long time, but it too will slowly succumb to the radiation bombardment
of the interplanetary environment. Much of the Roadster and Starman will end up in shreds and
dust, probably dispersed by centrifugal force (the Roadster rotates on itself
in just under five minutes, and its gravity is irrelevant). In a few years, say the pessimists,
the Tesla will be a faded skeleton of metal and shreds of plastic, with a yellowed windshield.
In addition, Starman and his car are traveling in an orbit whose distance from the Sun varies
with a period of 557 days from 150 to 250 million kilometers.
Which means that aircraft and pilot will go through cycles of heating and cooling
that will tend to degrade all materials of the Tesla, even those inorganic as glass and metals.
All of this will happen fairly quickly, say a decade or so.
But for Tesla and its passenger, the trouble is just beginning. At longer times, say from now
to the end of the century they will have to fight with the flow of micrometeoroids that continuously
crosses the interplanetary space. If we assume for convenience the data for near Earth Space, every
square meter of Tesla will be hit on average every century by a grain at least one millimeter wide.
That sounds like nothing, but when a grain of sand passes through you at ten or twenty
kilometers per second, it can leave a hole nearly half a centimeter wide. In a couple of
centuries the wreckage of the Tesla and Starman will look like they came out of a gunfight.
In a few thousand years both will have collected the first impacts with bodies close to the
centimeter in size, capable of leaving craters the size of a fist. In a million years probably
one or more meteorites as large as a small pebble will hit what remains of Tesla, devastating it.
In short, in about one million years a specter will roam the Solar System:
the Tesla reduced to a pile of metal pierced and broken, with a windshield now completely
opaque and full of cracks and holes. In one or two places it is clear that the collision
with something big has dismembered some pieces. Small piles of dust here and there,
perhaps held back by electrostatic forces, will be what remains of Starman and the car's trim. An
extraterrestrial intercepting the Tesla would have a hard time figuring out what it is or was about.
At that point, Isaac Newton with his universal gravitation will be the biggest risk for Tesla.
A million years after the launch Musk's car will have completed more than five
hundred thousand orbits around the Sun, but how long can the carousel last?
The planets of the Solar System, especially Earth and Jupiter, with their gravitational fields
will slowly change the orbit of the Roadster, shortening or lengthening its period of
revolution. In the same way, also more subtle phenomena will act as the Yarkovsky effect, that
is the alteration of the orbits of small celestial bodies due to the pressure of thermal radiation.
In general, the possible scenarios are three. The Roadster could get closer and closer to the
Sun until it literally falls into it. Or it could be hurled away from the solar system and end up
in interstellar space. Or finally - less likely but entirely possible - it could hit a planet,
such as Mars or Earth. Predicting exactly what and when it will happen is
notoriously difficult, as gravitational systems with more than three bodies are chaotic systems,
where a tiny error on the initial data leads to completely different predictions.
If the remains of the Roadster will not crash or will not be ejected into interstellar space,
then the Sun will decide its fate, even if only in billions of years.
In fact, our star will become brighter and brighter until, 5 billion years from now, it
will rapidly evolve into a red giant, monstrously increasing its diameter to encompass the Earth
and in all probability also Tesla. The metallic remnants will first melt,
becoming an orbiting droplet of liquid metal, and then disintegrate in the solar atmosphere. At this
point, Starman's journey is over. By diving into a star, he will do justice to his name.
If, on the other hand, the Roadster finds itself exiled to interstellar space, its
remains could survive for a long time. It would become an interstellar asteroid like 'Oumuamua.
It might reach another solar system and perhaps be intercepted by some intelligent species. But
unfortunately, it is very unlikely to happen. Almost certainly its next encounter with a star
system will happen in an inconceivable number of years and by that time
all stars will have become black holes or moribund white dwarfs. The Tesla wreckage will then wander
forever in the darkness within the galaxy, slowly consumed by the incessant erosion of cosmic dust.
If they manage to avoid being swallowed by a black hole, the last remnants of the
Tesla will also end up in dust, in a universe far colder and darker than the one we know.
But the Roadster's main appeal has never been its physical state.
The iconic image of "Starman" flying through space, with Earth as a backdrop,
inspired audience members and sparked excitement about the new space race.
To imagine where "Starman" might fly is to imagine where humanity might go.
And that's why, although very far away and practically unobservable, we think it's
important that each of us can at least know its approximate position in the sky, so that we can
accompany it with our thoughts in its melancholic and suggestive journey in the Solar System.
But in cases like these, how to do it? We know the celestial coordinates of Starman, hour by hour
(right ascension and declination)... but for those who do not have a deep astronomical knowledge,
these coordinates are very obscure and impractical.
The only way to be sure to look in the right direction is then to
relate the position of Starman with that of another celestial object, but that is
clearly visible and recognizable by anyone ... And what is there in the night sky more
easily recognizable than the Moon? Nothing! And it is precisely for this reason that we invite
all of you, on the evening of August 14th at 10:00 pm local time in New York City, to be found with
your eyes turned towards the southwest horizon. At an altitude of about 13 degrees above
the horizon, a beautiful First Quarter Moon will be visible.
Well, less than 5 degrees east of the Moon, and at the same altitude,
that will be the point where you will have to look to "perceive" the invisible presence of Starman.
The Tesla at that time will be 178 million kilometers away from the Earth, moving
away at a speed of 23 kilometers per second. This is valid for the inhabitants of the region
around New York, but with slight differences in time and position, it will also be valid for many
other places on Earth. In Rome, at the same time of 22:00, the angular distance of Starman from
the Moon will be 7.5°, in Moscow 8.5°, etc. To orientate yourself even better, go back to
look at the celestial map that we proposed at the beginning, and compare all the various references.
As you can see, in addition to the Moon, Starman will enjoy the company of extraordinary
summer constellations such as Scorpio as it moves away from your sight, diving deeper and
deeper into the constellation Libra. Goodbye starman, have a good trip!