Predicting Starman’s Return To Earth

There’s a Starman, waiting in the sky. He’d like to come and meet us, but he’ll have to wait several million years until the Yarkovsky effect brings him around to Earth again.

In case you’ve been living under a rock for the past few weeks, SpaceX recently launched a car into space. This caused much consternation and hand-wringing, but we got some really cool pictures of side boosters landing simultaneously. The test launch for the Falcon Heavy successfully lobbed a Tesla Roadster into deep space with an orbit extending out into the asteroid belt. During the launch coverage, SpaceX said the car would orbit for Billions of years. This might not be true; a recent analysis of the random walk of cars revealed a significant probability of hitting Earth or Venus over the next Million years.

The analysis of the Tesla Roadster relies on the ephemerides provided by JPL’s Horizons database (2018-017A), and predicts the orbit over several hundred years. In the short term — a thousand years or so — there is little chance of a collision with anything. In 2091, however, the Tesla will find itself approaching Earth, and after that, the predicted orbits change drastically. As an aside, we should totally bring the Tesla back in 2091.

Even though the Tesla Roadster, its payload adapter, and the booster are inert objects floating in space right now, that doesn’t mean there aren’t forces acting on it. For small objects orbiting near the sun, the Yarkovsky effect is a huge influence on the orbit when measured on a timescale of millennia. In short, the Yarkovsky effect is a consequence of a spinning object being heated by the sun. As an object (a Tesla, or an asteroid) rotates, the side facing the sun heats up. As this side faces away from the sun, this heat is radiated out, imparting a tiny, tiny force. This force, over a period of millions of years, can send the Tesla into resonances with other planets, eventually sending it crashing into Earth, Venus, or the Sun.

The authors of this paper find there is a 6% chance the Tesla will collide with Earth and a 2.5% chance it will collide with Venus in the next one Million years. In three Million years, the probability of a collision with Earth is 11%. These are, according to the authors, extremely preliminary calculations and more observations are needed. If the Tesla were to hit the Earth, it’s doubtful whatever species populates the planet would notice; the mass of the Tesla is only 1250 Kg, and Earth flies through meteoroids weighing that much very frequently.

Photographing Starman From a Million Miles Away

Love it or loathe it, launching a sports car into space is a hell of a spectacle, and did a great job at focusing the spotlight on the Falcon Heavy spacecraft. This led [Rogelio] to wonder – would it be possible to snap a photo of Starman from Earth?

[Rogelio] isn’t new to the astrophotography game, possessing a capable twin-telescope rig with star tracking capabilities and chilled CCDs for reducing noise in low-light conditions. Identifying the location of the Tesla Roadster was made easier thanks to NASA JPL tracking the object and providing ephemeris data.

Imaging the Roadster took some commitment – from [Rogelio]’s chosen shooting location, it would only be visible between 3AM and 5:30AM. Initial attempts were unsuccessful, but after staying up all night, giving up wasn’t an option. A return visit days later was similarly hopeless, and scuppered by cloud cover.

It was only after significant analysis that the problem became clear – when calculating the ephemeris of the object on NASA’s website, [Rogelio] had used the standard coordinates instead of the actual imaging location. This created enough error and meant they were looking at the wrong spot. Thanks to the wide field of view of the telescopes, however, after further analysis – Starman was captured, not just in still, but in video!

[Rogelio]’s work is a great example of practical astronomy, and if you’re keen to get involved, why not consider building your own star tracking rig? Video after the break.

[Thanks to arnonymous for the tip! If that’s a nickname and not just a request to be anonymous but misspelled.]

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