Podcaster: Sabrina Stierwalt
Title: Everyday Einstein: Rock or Alien Probe?
Organization: Quick and Dirty Tips
Link: https://www.quickanddirtytips.com/everyday-einstein
This podcast has been published in: : https://www.quickanddirtytips.com/education/science/could-we-live-on-mars
Description: There’s a mysterious rock traveling through our solar system, and it’s making headlines again. Could it in fact not be a rock at all, but an alien probe? Let’s look at what the evidence has to say.
Bio:When not writing and recording podcasts for the Everyday Einstein show, Dr. Sabrina Stierwalt is an extragalactic astrophysicist at the California Institute of Technology and Adjunct Faculty at the University of Virginia. Before moving to Los Angeles, Sabrina received her PhD in Astronomy and Astrophysics from Cornell University. Sabrina earned a B.A. in Physics and Astronomy from UC Berkeley. She studies star formation and gas kinematics in interacting galaxies to better understand how galaxies form and evolve. She travels all over the world to observe the sky with world-class telescopes in Australia, India, Chile, and even on top of volcanoes in Hawaii.
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Transcript:
There’s a mysterious rock traveling through our solar system, and it’s making headlines again. Could it in fact not be a rock at all, but an alien probe? Let’s look at what the evidence has to say.
A few days ago, I got an early morning text from a friend: “news says we have an alien probe. Please advise.” Part of my duty as an astrophysicist is, of course, to be able to warn my friends of an alien invasion—so I was worried I had failed. The press often sensationalizes headlines in order to get eyeballs on their articles, but a quick search told me this claim was even coming from astronomers. This deserved a proper investigation!
There was much excitement when astronomers discovered the first interstellar visitor—that is, the first object to visit our solar system from another star system—in October of 2017. Where had it been? What had it seen? Where was it headed? I mentioned the discovery here on Everyday Einstein. The strangely elongated rock was traveling too fast, around 25 kilometers per second, to be a member-in-good-standing of our own asteroid belt so it must be just passing through. It was named ‘Oumuamua (apostrophe intentional) meaning “first scout” in Hawaiian.
So what’s all the fuss about now? A year later, ‘Oumuamua is making headlines again due to a paper suggesting that it could be an alien probe inserted here by an outside intelligent civilization. Let’s take a look at the evidence for why this may (or may not) be the case.
What do we know about ‘Oumuamua?
The truth is ‘Oumuamua is weird. While we are used to seeing mostly round or nearly round objects in space, this rock is elongated at an estimated 800 by 100 feet in size. It dims and brightens in a regular cycle, suggesting it may be hurtling through space end-over-end. (Think of a tumbling baton.) Also weird: when first discovered, astronomers thought it was most likely a comet. But observations with the Hubble Space Telescope showed the object did not have the typical tail of gas that comets have when their surface ices are turned to gas by the sun’s heat.
And, of course, its unusual orbit suggests that it has been traveling through interstellar space before entering our solar system, only to leave us again in the future. We know this because it is traveling too fast for the gravitational pull of all the major objects in the solar system to be able to hold on to it.
Here’s where the new theory-based paper comes in. The authors calculated whether light from the Sun could be forceful enough to be responsible for pushing ‘Oumuamua along. When photons exert a pressure on an object, it is called radiation pressure, which is a well-studied and well-understood phenomenon—so nothing unusual. Their calculations showed that it would be rather hard for radiation pressure to exert enough force to push along a wide, elongated space baton (remember that size estimate of 800 by 100 feet), but radiation pressure could do the trick for an object that was shaped more like a very thin, flat sheet. Maybe we were wrong about the size.
We don’t really have many astronomical objects that are 100 feet (or about 30 meters) by 1 millimeter thick as the authors suggest would be needed, but we are building them. Solar
sails—also called light sails—are being developed as a way to accelerate a spaceship (through encouraging the push of radiation pressure) without having to tote along heavy, expensive, and quickly-depleted fuel. This is the kind of acceleration you would need for interstellar travel. If you’re curious to learn more, the Planetary Society has some great animations showing their light sail plans.
So is ‘Oumuamua an alien probe?
If our interstellar visitor is indeed some kind of light sail, that could explain how it got here (a mystery), why it has such a weird shape (a bigger mystery), and how it can move so fast (perhaps the biggest mystery). However, several other properties still don’t fit the light sail explanation. For example, we don’t expect light sails to change in brightness with regularity as ‘Oumuamua does.
There are also several possible explanations for how ‘Oumuamua might still be a comet—the simplest explanation—even though we did not see the telltale, well, tail of emission with Hubble. We could have been looking at the wrong wavelength. Our most sensitive telescopes, like Hubble, are at optical wavelengths, so we relied on optical images of the object to look for the cometary tale. The surface ice on ‘Oumuamua could instead be better at emitting at infrared wavelengths. ‘Oumuamua might also simply be a weary traveler that has lost most of its dust already, making it so that whatever emission it has left is too faint for us to see.
The speed of ‘Oumuamua is also somewhat of a problem. Yes, the light sail explanation explains how it could reach a speed of 25 kilometers per second. That’s fast for a solar system object, but it is still far slower than we would expect from a light sail sent purposefully to our solar system to either monitor us or send us a message. As the Planetary Society explains, the force they expect from the Sun on their light sail is about the equivalent of the force exerted by a paper clip on the palm of your hand. That doesn’t sound like much, but it’s enough to increase the light sail’s speed significantly over its assumed long travel time. To make interstellar travel possible, speeds more on the order of 60,000 kilometers per second are expected. So we can’t rule out an alien probe, but the possibility raises at least as many questions as it solves.
Is there life on other planets or are we alone in the universe? This question is one of the fundamental unanswered questions with an answer that links all of humanity. It drives us to explore and search for other planets that resemble our own Earth both in and out of our solar system and inspires large efforts like SETI, the Search for Extra Terrestrial Intelligence. We are so eager to learn the answer that sometimes we may look too hard for it.
End of podcast:
365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by Planetary Science Institute. Audio post-production by Richard Drumm. Bandwidth donated by libsyn.com and wizzard media. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. This year we will celebrates the Year of Everyday Astronomers as we embrace Amateur Astronomer contributions and the importance of citizen science. Join us and share your story. Until tomorrow! Goodbye!