BAN #311: Apophis impact no longer an immediate threat, Numerology, Live talk

05 April 2021   Issue #311

[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]

Subscribers have a big impact on me right now.

Upcoming Appearances/Shameless Self-Promotion

Where I’ll be doing things you can watch and listen to or read about

On Thursday, April 8, I’ll be giving my “Strange New Worlds” for the Vancouver branch of the Royal Canadian Astronomical Society! This event will be streamed live, and is free. Free, I say!

You can watch it on their YouTube channel live. There’s no direct link yet as I write this, but if you go to their channel shortly before the talk the video link will be there. The talk starts at 19:30 Pacific time. I hope y’all will join in! I love giving this talk; it’s all about exoplanets and how the Earth fits into the scheme of what we see in the galaxy. Is Earth special? Watch and find out!

Random Thoughts

Stuff I think about in the shower, typically

This is BAN Issue #311. That may mean nothing to you, but to me, well.

Are there any numbers that stick out to you when you see them? For whatever reason. Maybe it’s your birthday, or your favorite number, or some sequence of numbers in pi.

For me, one of those numbers is 311, and it’s for just about the silliest reason possible: It’s the canonical number of people who were on Moonbase Alpha when it blasted out of Earth orbit on September 13, 1999.

Or so it did in “Space: 1999”, my favorite show when I was a kid. I don’t remember when that number was given, but I do remember watching the show every week with a friend and whenever someone was killed on the show — a frequent occurrence, given the nature of scifi TV at the time — we’d count down from 311. On the rare occasion someone new was taken on, we’d add to the remaining count, but that was much more rare.

This’ll help.

Like I said, silly. Well, to you, maybe, but to me the number 311 still stands out when it pops up. But I imagine this happens with lots of folks. Maybe for you it’s a different number (at least I’d bet that way) or a word, a name, a shape. Whatever, it’s yours. I wonder how common this is, because I know it’s true for some people I know.

I have no real point to make here, except that our brains are silly. I do enjoy pointing that out.

Blog Jam

What I’ve recently written on the blog, ICYMI

[Artwork depicting the moment of collision between two neutron stars. The resulting explosion is quite large, and creates a black hole. From Wednesday’s article. Credit: Dana Berry, SkyWorks Digital, Inc.]

Monday 29 March, 2021: Meet G117-B15A: the most stable optical clock in the Universe

Tuesday 30 March, 2021: The birth of a little black hole may have revealed a much bigger black hole

Wednesday 31 March, 2021: The interstellar comet Borisov was shiny and new when it passed through our solar system

Thursday 1 April, 2021: Terrascope: The Whole Earth Telescope

Friday 2 April, 2021: Hey Mars, what’s shakin’?

Space news

Space is big. That’s why we call it “space”

Hey, some good news! An Earth impact by the pants-wettingly large asteroid Apophis has been ruled out for the next century at least.


[The orbit of 2004 MN4 (Apophis) takes it extremely close to Earth. This shows its position on 6 March 2021 when it was observed with radar. Credit: NASA/JPL-Caltech]

Apophis was discovered in 2004 (its full name is 2004 MN4 (Apophis)) and was quickly found to be a potentially hazardous object; its elliptical orbit takes it as close to the Sun as Venus and just farther than Earth. That is not necessarily a problem, but it so happens that its orbit literally intersects Earth’s, meaning if it’s at that intersection (technically called a node) as the same time Earth is, well… bang.

Apophis is over 330 meters across. So it would be a very large bang. Like, over a thousand megatons of explosion bad.

That made Apophis the poster child for asteroid impacts. Heck, even this guy did a TED talk about it:

We’ve known for some time there would be a close encounter with Apophis in 2029, and for a while after its discovery there was a small but non-zero chance it would hit us. More observations showed it would miss, but still come extremely close to us. We now know it will pass the Earth at a distance of about 32,000 km above Earth’s surface — closer than geosynchronous satellites! It’s definitely a miss, but there was then some concern about how the Earth’s gravity would affect the asteroid orbit; if it’s just right it could swing back around and hit us in 2036.

However, in 2013 further observations ruled that out. Yay!

[Animation of the path of asteroid Apophis as it passes Earth in 2029; the overall orbit will change substantially. It currently goes from roughly the orbit of Venus to Earth; after 2029 it will go from Earth to halfway to the orbit of Mars. Credit: ESA/NEO Coordination Centre]

But there was still a chance of impact in 2068. The odds were low, but again non-zero.

But here’s the good news: Using radar combined with optical observations, not only is the 2068 date ruled out for impact, we can confidently state that there won’t any chance of an impact for at least a century.


The problem is that any small uncertainty in the measurement of an asteroid’s position and velocity now just gets bigger projected into the future. But in early March 2021 Apophis passed about 17 million km from Earth, allowing astronomers to get radar observations (using NASA’s Goldstone dish and the huge 100-meter Green Bank radio telescope). They pinged the asteroid with radio waves, measuring how long it takes them to get to the asteroid and back. Together with optical images that yielded extremely precise measurements, showing that no impact will occur for a long, long time.

To make this point even better, Apophis was removed from both NASA’s Sentry page and the ESA’s Risk List.

There are still plenty of rocks out there that can hit us, but most are small and all have very low chances of impacting us.

Still, we need to keep an eye out. The asteroid that burned up and exploded over Russia in 2015 was only 19 meters across, so it doesn’t take a huge rock to do significant damage. The closer we watch the skies, the better.

Et alia

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