This video is supported by KiwiCo.
On the 6th of February 2018, the Falcon Heavy launched Starman and his Tesla Roadster into space.
After leaving Earth, Starman ended up on an orbit around the sun.
The chances of Starman coming back to Earth are extremely low.
Its orbit isn’t expected to intersect Earth until the year 2047.
Even when this happens, it will only pass by briefly at a distance of 2 million miles.
After this close encounter, it will continue on its orbit around the sun, not returning
to Earth for at least another few decades.
Throughout the history of spaceflight, we have launched hundreds of objects beyond Earth’s orbit.
Some objects like the Voyager space probes, have even gone fast enough to leave the solar system.
Once something is sent into space, that is usually the last goodbye.
And unless something is specifically designed to return, these objects are destined to spend
the rest of their lives in space.
Natural objects however enter Earth’s atmosphere everyday.
Most of these are large fragments of asteroids that broke apart a long time ago in our Solar System.
Some of these are large enough to survive the intense journey through Earth’s atmosphere
and reach the surface.
Back in September of this year, astronomers were observing some of these asteroids using
the NASA survey telescope on the island of Maui.
This specific group of astronomers were focusing on asteroids heading in the direction of Earth.
They discovered an object that was heading towards Earth with some unusual characteristics.
This object flew past our Moon at 3,000km/h, much slower than the typical speed of an asteroid,
which can sometimes reach tens of thousands of km/h.
Most asteroids have a more oval-shaped orbit, on a plane that’s tilted compared to Earth.
Initial calculations of this object showed that it had a very circular orbit around the
sun, similar to that of Earth.
On further inspection, the orbital plane of this object wasn’t tilted, and in fact perfectly
matched the orbital plane of Earth.
This low velocity paired with an Earth-like orbit made the astronomers think that this
wasn't an asteroid, but in fact an artificial object that originated from Earth.
They continued to observe this object and gave it the name 2020SO.
After further analysis and tracing back its orbit, they found that object 2020 made a
close approach to Earth back in 1966.
Looking through the launch archives from this time period, they found a mission that lined
up with this almost perfectly: the Surveyor 2 mission.
Lifting off from Cape Canaveral on an Atlas-Centaur rocket, Surveyor 2 headed for the Moon.
It was designed to conduct experiments on the Lunar surface and send back detailed images
which would help NASA plan for the upcoming Apollo missions.
After all, humans were just 3 years away from walking on the Moon and yet very little was
known about the world they would be entering.
After launch, the Centaur upper stage placed the spacecraft on a path towards the Moon.
But as Surveyor tried to refine it’s path, one of its thrusters failed and caused the
spacecraft to lose control, until it hit the Moon at almost 10,000km/h.
The Centaur upper stage continued on, flying past the Moon and entering into an unknown
orbit around the sun.
For decades, this rocket booster was out there doing laps around the sun.
But it’s orbit was slowly being changed by the continuous pressure from the sun.
The radiation which blasts out from the Sun exerts a small but constant force on objects
in space, like a very gentle breeze.
Since the Centaur booster is essentially an empty metal tube, it’s very lightweight
but still has a large surface area.
This makes it much more susceptible to the solar winds than a dense and heavy asteroid.
After observing this gradual change in orbit, astronomers confirmed that this couldn’t
be an asteroid and it must be something made by humans.
But the astronomers still weren’t sure if this object really was the Centaur rocket
from the 60’s making a surprise return to Earth.
2020 was on a trajectory to enter Earth’s orbit in November - and the astronomers calculated
that it would make several close approaches during its stay, before returning to an orbit
around the Sun in March.
This would be a great chance to observe the object in more detail and determine if it
really was the Centaur rocket.
However, this object was incredibly faint and required some of the world's most powerful
telescopes to even see it.
At its closest approach, it would reach an apparent magnitude of just 14.
On the magnitude scale, objects only become visible to the human eye once they reach 6 or below.
To put this into perspective, most of the planets in our solar system have a magnitude
below 1 and even they can be difficult to spot with the naked eye.
The only way the scientists could prove this was the Centaur rocket would be to find out
if it was made from the same material, 301 stainless steel.
In order to do this, scientists took over NASA’s infrared telescope in Hawaii and
began doing spectroscopy observations.
This telescope has a 3 meter wide mirror and is located at an altitude of 4,000m on top of a mountain.
It can measure a wide range of wavelengths in the infrared spectrum, allowing it to perform
spectroscopy observations.
This technique is often used to study the atmosphere of distant exoplanetes, to determine
what elements they are made of.
As a planet passes in front of its star, the molecules in the atmosphere absorb light at
specific wavelengths.
By observing these dips at specific wavelengths, we can compare it to the data we have here
on Earth and determine which atoms and molecules are present in the atmosphere.
The same technique can be used on a solid object to determine its material.
The atoms and molecules that make up stainless steel will emit and absorb light at very specific wavelengths.
So, the scientists took spectral measurements of object 2020 and compared it to measurements
made of stainless steel here on Earth.
With this data, the scientists could compare the two measurements and see if they had similar
light behaviour.
The data showed some similarities, but the match was far from perfect.
They realized that the difference in results could have been from observing ordinary stainless
steel against stainless steel which had been exposed to the harsh conditions of outer space for 54 years.
In order to get a real match, they would need to compare it to a piece of stainless steel
that has also seen the harshness of space.
Luckily, there have been 245 Centaur launches since 1962 - and many of the old stages still
remain in Earth’s orbit.
But observing one of these old rocket stages for long enough would be a massive challenge.
Objects in Earth’s orbit can move across the sky at an incredible speed.
This means NASA’s infrared telescope would struggle to lock onto the object for long
enough to get a good amount of data.
They chose to observe a Centaur rocket stage which launched in 1971, taking a communication
satellite into orbit.
Despite the challenge, the scientists managed to lock onto the 49 year old rocket and gather
all the data they needed.
This happened on the same day that object 2020 made its closest approach to Earth.
The data came back and the spectrum graph of this old rocket stage perfectly matched
that of object 2020.
This proved that object 2020 was made of 301 stainless steel and was undoubtedly the lost
Centaur booster from 1966.
So as we continue to launch more and more objects into space, our ability to detect
which objects are heading towards Earth will become increasingly important.
As our presence in space increases and our technology becomes more advanced, observing
objects like this will become much more routine.
For object 2020, it will leave Earth’s orbit in March and continue orbiting the sun until
it eventually returns to Earth again in the distant future.
Like Starman, these objects are on a journey that us humans could never imagine.
But due to the laws of physics, they always end up coming home at some point.
When 2020 eventually returns to Earth again, who knows how far our technology will have
advanced and what kind of things we will be doing in space.
But it's up to us to teach the next generation of scientists and engineers about the wonders of space.
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