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How did earth get the ingredients for life? A new discovery from Comet 67P might hold some answers. And learn where to find Mars in the night sky from 75 million kilometers away.

Host: Hank Green

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Hank: Scientists are always looking for clues about how life developed on Earth. And last week, they announced a discovery that’s helping us figure it out: Comet 67P has an amino acid on it called glycine -- one of the building blocks of proteins, and a key ingredient for life as we know it!

We know a fair amount about how life evolved on Earth. But we don’t know much about how the ingredients for life -- the molecules that were first incorporated into living cells -- got here in the first place. Scientists are pretty sure these molecules came from other objects in space, like asteroids and comets, that smashed into Earth. But, so far, we’ve only found a few of those molecules outside of Earth.

Then, last week, astronomers announced in the journal Science Advances that, using instruments on the Rosetta probe, they’d detected the amino acid glycine in the gas and dust surrounding 67P -- along with two molecules used to make it, called methylamine and ethylamine. They also found phosphorus -- which is used to form DNA and our cell membranes, among other things.

So all of those molecules are ingredients needed for life as we know it. Now, this is the first time phosphorus has ever been found on a comet! But we’ve detected glycine once before. Back in 2009, a separate group of researchers found evidence for it in samples taken from Comet Wild 2, which the Stardust probe collected during a flyby.

But there were issues with those samples: at least some of the glycine researchers detected might have come from contamination when the samples were brought back to Earth. Rosetta’s findings don’t have that problem -- the researchers can rule out contamination from Earth because Rosetta wasn’t detecting glycine in the measurements it took before it got to the comet.

If we were going to find any amino acids on 67P, glycine is the one that makes the most sense. For one thing, it’s the simplest of all the amino acids It’s also the only amino acid that can form without the presence of liquid water -- and Comet 67P is cold and dry. So was the early solar system. So, we now know that more of the molecules necessary for life exist off of Earth -- which could explain how they got here.

And, if impacts by comets and asteroids did bring those molecules to Earth, it’s possible that they brought them to other worlds, too. And speaking of other worlds: if you’ve looked up at the night sky recently, you might’ve noticed an unusually bright point of light. Well that’s because Mars is only 75 million kilometers away -- the closest it’s been to Earth since 2005.

Technically, the closest approach of the two planets was this past Monday night, May 30th. But we’re still pretty close, and Mars will stay very bright in the night sky until around mid-June. It’ll be among the stars of the constellation Scorpius, in the southern sky, and it should be visible from both the northern and southern hemispheres -- though it’ll be higher in the sky in the south.

On average, Mars is about 225 million kilometers from Earth. But both Earth and Mars are orbiting the Sun, so their distance from each other depends on where they are in their orbits. And roughly every two years, they line up for their closest approach -- which is why most Mars missions are launched every two years, to take advantage of the shorter distance.

But that closest approach can be a different distance every time, because the planets’ orbits are kinda wonky. They’re ellipses, which means each planet can be closer or farther from the Sun, depending where it is in its orbit. The orbits are also tilted differently.

So, sometimes Earth and Mars line up in a spot where their orbits are very close together. Other times, they’re a little farther apart. In 2003, for example, we were only 56 million kilometers from Mars -- the closest we’ve been in 60,000 years, and the closest we will be until the year 2287.

The next closest approach will be in July 2018, when we’ll be about 57 million kilometers away. So, for the next week or two, don’t forget to look up. And if you’re really aching to send a probe to Mars, now is the time, so get your act together.

And thank you for watching this episode of SciShow Space News, and especially to all of our patrons on Patreon who make this show possible. If you want to be one of those people and help us keep making episodes like this, you can go to, and don’t forget to go to and subscribe!