Number of known asteroids reaches 1 million

[mfb]

TL;DR Summary

1 million asteroids have been discovered in the Solar System

1,002,726 or 993,960 known asteroids depending on the database.

We find asteroids faster than ever before. By 1921 astronomers knew 1000, then it took almost 70 years to extend that to 10,000 (1989). Just 16 years later we reached 100,000 (in 2005), and 15 more years later we reached 1 million. Early discoveries were people looking at analog photos, but now most discoveries are done by computers analyzing giant datasets. Here is a table by discoverer.

Will we reach 10 million by 2035-2036, continuing the exponential trend? Gaia is expected to measure up to a million asteroids (to be published 2027 or so). Most of them will be known objects measured more precisely but the overlap won't be complete - we should also get many new objects. The Vera Rubin telescope is expected to add ~5 million more in the next 10 years. Some other programs will add 6-digit numbers here and there, probably, although they might have a lot of overlap with the Vera Rubin telescope. We'll see, could get close.

We can also expect a lot of progress with near Earth asteroids, i.e. asteroids that could come close to Earth. We know almost all over 1 km, now work is ongoing to find most over 140 m, but in parallel many smaller asteroids are being discovered as well. Down to ~20 m this has a practical use if we find them before an impact, but of course the larger ones are more dangerous.

 

[stefan r]

If the exponential trend in number of known asteroids continues [problematic assumption] then we can calculate the capabilities of our telescopes.

 

[mfb]

Many new discoveries are made with relatively small telescopes. Even the biggest discovery programs don't use the largest available telescopes: Spacewatch uses a 1.8 meter diameter main telescope, LINEAR uses a 1 meter main telescope, both have smaller telescopes for follow-up measurements. These programs found the most asteroids. Catalina ("CSS" in the list) has a 1.5 meter telescope and so on.

It's expected that there are about 1 million asteroids above ~700 meters in the asteroid belt. We don't know all of them and we know smaller ones, and there are also asteroids elsewhere, but that's a good number to keep in mind for the typical discovery. For 10 million we need to go down to ~150-200 meters. For 100 million we would need to go down to 50-100 meters.

If you want to collect the same light then the product of asteroid diameter and telescope diameter must be the same. Naively scaling things we need an 8-meter class telescope for 10 million. That's Vera Rubin, and the difference between "5 million new ones" and 10 million total is easily within the uncertainties of all these estimates. Increasing that by another factor 2-3 (for 100 million) is ~20 meters. We can build primary mirrors that large (it's about the size of GMT and half the diameter of ELT, both under construction), but that would need to be combined with a large field of view and a rapid motion between targets. But who knows what we can do by 2050.

 

[Vanadium 50]

At some point, the IAU is surely going to Pluto some of these asteroids (interesting that they have a "minor planet center" even though all but one of the asteroids are neither planets nor even dwarf planets) is a 1 km object an asteroid? Certainly. What about one micron? Certainly not. So somewhere they need to draw a line. Somewhere in the 10 m ballpark there will be more asteroids than people.

 

[Ibix]

At some point, the IAU is surely going to Pluto some of these asteroids (interesting that they have a "minor planet center" even though all but one of the asteroids are neither planets nor even dwarf planets) is a 1 km object an asteroid? Certainly. What about one micron? Certainly not. So somewhere they need to draw a line. Somewhere in the 10 m ballpark there will be more asteroids than people.

Wikipedia's article on asteroids suggests "meteoroid" is in use for small things that we'd call an asteroid if they were bigger. However it provides two references with different definitions of meteoroid - objects with diameters 100μm - 10m (Beech and Steel) and 10μm - 1m (Rubin and Grossman). The latter cites the former, but I don't know if either is authoritative (@davenn is our meteor man). "Micrometeoroid" seems to be in use for even smaller objects.

References (pasted from Wikipedia):

Beech, M.; Steel, D. (September 1995). "On the definition of the term meteoroid". Quarterly Journal of the Royal Astronomical Society. 36 (3): 281–284. Bibcode:1995QJRAS..36..281B.

Rubin, Alan E.; Grossman, Jeffrey N. (January 2010). "Meteorite and meteoroid: New comprehensive definitions". Meteoritics and Planetary Science. 45 (1): 114–122. Bibcode:2010M&PS...45..114R. doi:10.1111/j.1945-5100.2009.01009.x

 

[davenn]

is a 1 km object an asteroid?

Most definitely. Anything about 15 to 20m and over is deemed an asteroid. That includes the 2013 Chelyabinsk object
anything under that is deemed a meteoroid

 

[davenn]

Beech, M.; Steel, D. (September 1995). "On the definition of the term meteoroid". Quarterly Journal of the Royal Astronomical Society. 36 (3): 281–284. Bibcode:1995QJRAS..36..281B.

nothing readable on this link

Rubin, Alan E.; Grossman, Jeffrey N. (January 2010). "Meteorite and meteoroid: New comprehensive definitions". Meteoritics and Planetary Science. 45 (1): 114–122. Bibcode:2010M&PS...45..114R. doi:10.1111/j.1945-5100.2009.01009.x

A good link

 

[Vanadium 50]

anything under that is deemed a meteoroid

Do meteoroids get named?

 

[Keith_McClary]

 

[davenn]

Do meteoroids get named?

Not that I am aware of, probably because they are below the detection threshold spoken of in
that second article that @Ibix listed, that ~ 10m size

 

[mfb]

2015 TC₂₅ with a diameter of just 2 meters only has its systematic name, but it has its own Wikipedia page.

It won't come anywhere close to Earth again until 2089 when there is a small chance it will burn up in Earth's atmosphere.