Yes! It's me again, Emily Graslie of The Brain Scoop. Today, I want to tell you about a couple of near misses for our planet that you should really know about.

(Intro)

First, you hardcore SciShow News junkies, will remember last March when we told you about 2012DA14. An asteroid that was discovered last year to be heading towards Earth. Note I said towards Earth, not for Earth because, despite the media wide Pants-Wetting that took place last Spring, DA14 is not going to collide with our lovely planet. But it will come closer than any asteroid has in recorded history and you might even have a chance to glimpse it yourself. 

DA14 is only about 45 meters across and NASA's 'Near Earth Object Program' which tracks objects like this calculates that it will only come within 27,700 km of Earth - about 8000 km closer that the estimates we first reported to you last year. So close that the asteroid will actually come within the orbit of some man-made satellites and even though it poses no threat to us or any of our orbiting friends, like the moon or the International Space Station, it will be good for a game of astronomical hide and seek.

DA14 is so small that you probably won't be able to see it with the unaided eye but it will be visible with a small telescope or even binoculars. The best viewing will be from South East Asia and Australia at around 3.30 in the morning on February 16th local time, although observers may get a glimpse as far west as Eastern Europe. But sorry America, DA14 will make its closest approach at 2.30 in the afternoon Eastern Time on February 15th so by the time you get a view of the night sky, it'll have passed us by. If you miss it, you'll have to wait until 2020 when DA14 is scheduled to return and again, not hit us.

Speaking of near misses, I don't know if you noticed but our Solar System recently underwent some re-arranging and it turns out that Earth barely kept its place in the order of things.

See, astronomers recently revised their model for what they call the Circumstellar Habitable Zone. Is it a zone that is inhabited? No, its just the first in a star system that astronomers check when they start looking for extra terrestrial life. The zone is defined as being just the right distance from a star - not to hot, not to cold - for liquid water to exist because here on Earth, life really likes water so that's our best guess as to where it might like to hang out elsewhere. 

Last week a group of geoscientists, astronomers and astrobiologists from Penn State University and NASA's Goddard Space Flight Center said that they'd revised the formula that astronomers use to find the habitable zone for each star. Their revisions reflect what we've learnt about how things like water and carbon dioxide absorb radiation to make planets hotter. When they factored in these new findings, they found that planets closer to their stars are probably hotter than we'd assumed - some of them too hot for liquid water and some planets that we thought were too far and too cold, might actually be warm enough to have water. So the whole zone basically took a step away from the heat source.

Now, we don't know for sure that life needs water - as Penn State geoscientist Ravi Kopparapu, who initiated the revision, pointed out, there could be silicon-based lifeforms, like on Star Trek and why not? I mean, even on Earth we have extremophiles, organisms that exist in crazy conditions like in terrific heat or pressure and even without liquid water. But water-based lifeforms are still are best bet because we recognize them and their signs. We don't know what signs say silicon-based lifeforms would leave. 

So where do we look for them?

The new model says the best place to look for water is between 0.99 and 1.7 astronomical units from a star. 1 AU is the distance between Earth and the Sun and the standard astronomers use to measure planetary orbits.

This new definition doesn't change which planets within our own Solar System are within the zone - its still just Earth and Mars. But since the Solar System's habitable zone starts at 0.99 AUs, that means that Earth barely makes the cut.

We're on the hottest edge of the habitable zone, so shouldn't we be sweltering here?

Well, yes but we have clouds that reflect radiation so we're not as hot as really far away alien astronomers might think we'd be. And that might be the case for many planets. Lots of things may affect their temperature - mass, cloud cover, orbit shapes, axis, what kind of star they're orbiting.

As we get better at detecting new planets, nearly 800 and counting, we're learning more about how to study these features so we can narrow our search for the most habitable ones.

Thanks for joining me for SciShow News, if you have tips, ideas or any nice recipes you'd like to share you can find us on Facebook, Twitter and always in the comments below.