- 4339 - ASTEROIDS - odds for close encounter? In 2021 Earth had more than 100 close encounters with large asteroids. What are the odds of a direct hit in the near future? Asteroids are chunks of rock left over from the formation of our Solar System.
------------------------- 4339 - ASTEROIDS - odds for close encounter?
- Approximately half a billion asteroids with
sizes greater than four meters in diameter orbit the Sun, traveling through our
Solar System at speeds up to about 30 kilometers per second, about the same
speed as Earth.
-
- About 65 million years ago, life on Earth was
brought to its knees by what was likely the impact of a big asteroid, killing
off most dinosaurs. Even a four-meter object traveling at a relative speed of
up to 60 kilometers per second hit us.
-
- There are far more small asteroids than
large asteroids, and small asteroids cause much less damage than large
asteroids. Asteroid statistics and the
threats posed by asteroids of different sizes. NEOs are “near-Earth objects”,
any small body in the Solar System whose orbit brings it close to our planet.
-
- Earth experiences frequent but low-impact
collisions with small asteroids, and rare but high-impact collisions with big
asteroids. In most cases, the smallest asteroids largely break up when they hit
Earth’s atmosphere, and don’t even make it down to the surface.
-
- When a small asteroid, or “meteoroid” which
is an object smaller than an asteroid, hits Earth’s atmosphere, it produces a
spectacular “fireball”, a very
long-lasting and bright version of a shooting star, or meteor. If any surviving
bits of the object hit the ground, they are called “meteorites”. Most of the
object burns up in the atmosphere.
-
- A four-meter asteroid hits us about once per
year, on average. If you doubled that
surface area, you’d get two per year. Earth’s radius is 6,400 km. A sphere with
twice the surface area has a radius of 9,000 km. So, approximately once per
year, a four-meter asteroid will come within 2,600 km of the surface of Earth.
-
- Double the surface area again and you could
expect two per year within 6,400 km of Earth’s surface, and so on. This tallies
pretty well with recent records of close approaches.
-
- A few thousand kilometers is a pretty big distance
for objects a handful of meters in size, but most of the asteroids covered in
the media are passing at much, much larger distances. Astronomers consider anything passing closer
than the Moon, 300,000 km, to be a “close approach”. “Close” for an
astronomer is not generally what a member of the public would call “close”.
-
- In 2022 there were 126 close approaches, and
in 2023 we’ve had 50.
-
- Now, consider really big asteroids, bigger
than one kilometer in diameter. The same highly simplified logic as above can
be applied. For every such impact that could threaten civilization, occurring
once every half a million years or so, we could expect thousands of near misses
(closer than the Moon) in the same period of time.
-
- Such an event will occur in 2029, when
asteroid ”53814 (2001 WN5)” will pass 248,700 km from Earth.
-
- Approximately 95% of asteroids of size
greater than one kilometer are estimated to have already been discovered, and
the skies are constantly being searched for the remaining 5%. When a new one is
found, astronomers take extensive observations to assess any threat to Earth.
-
- The “Torino Scale” categorises predicted
threats up to 100 years into the future, the scale being from 0 (no hazard) to
10 (certain collision with big object).
-
- Currently, all known objects have a rating
of zero. No known object to date has had a rating above 4 (a close encounter,
meriting attention by astronomers).
-
- Technology has advanced to the point we have
a chance to do something if we ever do face a big number on the Torino Scale.
Recently, the DART mission collided a spacecraft into an asteroid, changing its
trajectory. In the future, it is plausible that such an action, with enough
lead time, could help to protect Earth from collision. ( In the meantime it makes for good movies.)
-
- “Centaurs” are small planetary bodies that
orbit between Jupiter and Neptune and have baffled astronomers for sharing
characteristics with both asteroids and comets.
-
- James Webb Space Telescope (JWST) has
conducted a first-time detection of carbon dioxide in a Centaur, this one
designated “39P/Oterma”. A Centaur is a small planetary body that orbits
between Jupiter and Neptune and frequently crosses the orbits of one or more of
the gas giant planets within our solar system. -
- While no Centaur has been imaged up-close,
they typically exhibit a combination of attributes between comets and
asteroids. While carbon monoxide has been detected in two known centaurs, this
recent discovery could mark a turning point in how scientists understand the
formation, evolution, and composition of not only Centaurs, but of the early
solar system, as well.
-
- Centaurs are important to study since they
are fairly well-preserved objects in space that can provide insight on the
chemical composition and physical processes of the early solar system.
-
- While “39P/Oterma” has long been classified
as an inactive comet, it currently exhibits a Centaur-like orbit between
Jupiter and Saturn, meaning it doesn’t approach the Sun, and has a radius of
approximately 1.37 to 1.55 miles.
-
- “39P/Oterma” is an active centaur. That is a centaur that develops a coma and a
tail like a normal comet. After
analyzing the JWST NIRSpec data, the researchers confirmed the first detection
of carbon dioxide in any Centaur, and the lowest amount of carbon dioxide ever
detected in any Centaur or comet.
-
- They also did not detect traces of water or
carbon monoxide, which are traditionally detected in Centaurs, specifically
“29P/Schwassmann-Wachmann 1” (29P/SW1), another Centaur that shares
approximately the same AU distance as 39P/Oterma.
-
- This difference in chemical behavior could
be from the very different sizes of Centaurs 29P and 39P, or from having different
orbital histories, or starting out with different compositions, or possibly a
combination of all of these.
-
- The finding of carbon dioxide in a Centaur
could be a game changer in terms of understanding the compositions and
characteristics of Centaurs, asteroids, and comets throughout the solar system,
along with potentially gaining better insight into the formation and evolution
of the solar system.
-
-
February 4, 2023 ASTEROIDS
- odds for close encounter? 4339
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--------------------- --- Monday, February 5,
2024
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