# How was the 18 December 2018 Bering Sea Fireball detected and characterized? Was it a serendipity or a weather satellite?

The map at Fireball and Bolide Data is reproduced in the BBC News article US detects huge meteor explosion with the 2013 Chelyabinsk event and the recent 18-Dec0281 Bering Sea event annotated.

The article goes on to say that the 18 December 2018 event wasn't widely acknowledged or reported in the news because it wasn't noticed.

This tweet points out that the Japanese weather satellite Himawari spotted the fireball in one of its images.

I'm wondering if this is how the 18 December 2018 fireball was discovered, or if it was identified by methods dedicated to detecting and characterizing fireballs.

Question: How was the 18 December 2018 Bering Sea Fireball detected and characterized? Was it serendipity, a weather satellite, or is there a fireball detection system of some kind in place?

above x2: From tweet. Himawari weather satellite.

below: From BBC CNEOS/NASA.

• Wow! that is a neat photo, the bolide looks to be coming down vertically, and its trail is even casting a shadow on the cloud layer below – Dave Gremlin Mar 18 '19 at 15:02
• From the linked article: "Military satellites picked up the blast last year; Nasa was notified of the event by the US Air Force." – Chris Mar 18 '19 at 15:14
• @Chris good catch, I wonder if it was serendipity, and also if that's our de facto "fireball detection network" – uhoh Mar 18 '19 at 15:17
• It's probably ballistic missile detection systems, in which case the answer is "it's classified" and "I could tell you, but then I'd have to waterboard you". – GdD Mar 18 '19 at 16:25
• Probably IR sats like SBIRS or DSP - intended to see missile launches. – Organic Marble Mar 18 '19 at 16:36

There is a network of satellites designed to detect ballistic missile launches. The key feature in each of these is very high temperatures moving at fast speeds. Thus, the easiest way to look for them is to look in the infrared for relatively high temperatures. It just so turns out that this is exactly the same kind of thing that an asteroid impact in the atmosphere will produce, and thus they can be confused for the same. The US government frequently provides such data to NASA, however, they do not provide the raw data, due to the sensitive nature of such things. A few interesting sources of information:

https://www.space.com/20310-russian-meteor-missile-attack-military.html

• It's quite important for the IR sats to be able to discriminate between meteor fireballs and missile launches.... – Organic Marble Mar 18 '19 at 17:01
• And fires and other similar things. But they should be relatively easy to detect, a meteor will be hot and fast, while a ballistic missile will be hot and slow, then getting faster, then cool (After the booster stops), and then warm right before impact (Reentry). – PearsonArtPhoto Mar 18 '19 at 17:03
• Ballistic missiles should be detected as early as possible shortly after launch but not short before impact. – Uwe Mar 18 '19 at 17:10
• Well, it should detect before impact, but it should have a detection on it earlier as well. Otherwise, what's the point? And at that point in time they look very different. – PearsonArtPhoto Mar 18 '19 at 17:11
• Hopefully missiles and meteors will be coming from different places, otherwise we're doomed. – uhoh Mar 18 '19 at 17:18

In the NPR News item and podcast Former Astronaut On Watching For Life-Destroying Objects From Space Reporter Lulu Garcia-Navarro interviews physicist and former NASA astronaut Ed Lu, currently the executive director of the B612 Foundation:

GARCIA-NAVARRO: So we only just learned of this meteor because NASA only just now put up the information on its website. That's pretty worrying, I must say.

LU: Well, actually, the incident was observed right away.

GARCIA-NAVARRO: Right.

LU: It's just that it was observed not by NASA but originally by a network of sensors used to detect atomic bomb explosions or nuclear-weapons tests around the world.

GARCIA-NAVARRO: Typically, how much notice do space agencies or observatories get about meteor or asteroid strikes?

LU: The typical notice for asteroid impacts on Earth is zero.

GARCIA-NAVARRO: Zero.

LU: And that's because the vast majority of asteroids are still untracked. This particular asteroid was quite small. It was only about 30 feet across. And the vast, vast majority of asteroids that small are not tracked.

Scott Manley just addressed this in his new video 173 Kiloton Explosion Over Bering Sea Was Asteroid Breaking Up a bit after 01:00:

But there are sensors all over the world looking for these big blasts because they look a lot like nuclear blasts; they have the same kind of energy, and there are many people who want to know if someone is testing nuclear weapons, so these things get picked up by that same network.

But the nature of this network means that we don’t really get the results from it very quickly.

So while this answer suggests it's a comparison to a rocket launch that's appropriate, Manley suggests that it's the comparison to a nuclear test of kilotons that's relevant, and that matches better the graphic in the question showing Energy in units of kiloton yield.