- 3852
- ASTEROIDS -
threaten our planet? Asteroids
hanging around Earth? Scientists are
discovering new near-Earth asteroids practically daily, with more than 27,000
identified to date.
-------------------- 3852 - ASTEROIDS - threaten our planet?
- Just how many space rocks out there
actually threaten our planet? NASA knows
of zero asteroids large enough to do meaningful damage on Earth and currently
on track to collide with our planet in the foreseeable future.
-
- But large asteroids hanging around
Earth? Scientists are discovering new
near-Earth asteroids practically daily, with more than 27,000 identified to
date.
-
- There is no known threat right now to
Earth. And while it may seem
paradoxical, the constant rise in near-Earth asteroid tallies turns out to be
the best news possible if you're worried about a potential asteroid impact.
-
- The art of protecting Earth from an asteroid
impact is called planetary defense, and there are two key stages to the
process. NASA's Double Asteroid Redirection Test (DART), launching in Feruary,
2023, is a mission designed to test the second stage of planetary defense,
diverting a threatening asteroid from crossing paths with Earth.
-
- But before anyone can even try to divert an
asteroid, scientists have to find the space rock and map out its orbit many
years into the future to realize that it will or may hit Earth.
-
- Keeping track of the actual asteroids,
identifying them and finding them is really crucial toward being able to do
anything about them in the future. Scientists have identified some 750,000
asteroids to date, but suspect there are millions of space rocks ricocheting
through the full solar system.
-
- Near
Earth that number comes down somewhat: Scientists have identified more
than 27,000 near-Earth asteroids, with new ones spotted daily. Those discoveries are thanks to a team of
instruments on Earth and in space that dedicate some or all of their time to
spotting and cataloging asteroids. The vast majority of these discoveries have
come since the late 1990s.
-
- The Catalina Sky Survey based in Arizona
specializes in catching smaller asteroids, the Pan-STARRS observatory in Hawaii
that excels at spotting faint objects, the NEOWISE space telescope that can see
the whole sky and the ATLAS telescopes in Hawaii that are tuned to the
fastest-moving objects.
-
- Wide-field survey telescopes are set up for
other purposes like for astrophysics investigations for instance, and then they
end up getting the asteroids that photobomb them.
-
- The Vera C. Rubin Observatory in Chile
begin observing in 2023; a space-based mission called NEO Surveyor is also in
development and scheduled to launch later this decade.
-
- Potentially hazardous asteroid identified
by early 2013, more than 1,400 objects in total. Today, scientists track more
than 2,000 potentially hazardous asteroids.
-
- If all those observations find that an
asteroid is over a certain brightness
and will come within 4.65 million miles of Earth, the object is
automatically dubbed a "potentially hazardous asteroid." (The
distance works out to one-twentieth of the average distance between Earth and
the sun.)
-
- But in most cases, despite the ominous
terminology, "potentially hazardous asteroids" may as well be called
"not currently hazardous asteroids." After all, these are the objects
that scientists have already found, and followed, and mapped, and forecast into
the future.
-
- Scientists believe they've found nearly all
the largest asteroids, those larger than 3,300 feet (1 km) across. and know
that these are the easiest to find anyway. And while tiny near-Earth asteroids
are plentiful and difficult to find, they are also the most likely to fall
apart harmlessly in Earth's atmosphere.
-
- So it's the middle size category of
asteroids, those more than 460 feet but less than 3,300 feet wide that most
worries planetary defense experts. As of
the end of 2020, estimates suggested scientists have found just 40% of
near-Earth objects of this size; this year has added 500 to the tally.
-
- NASA's planetary defense office estimates
that at the current pace, it will take scientists 30 more years to have
identified 90% of objects this size.
-
- The asteroid Itokawa is a pile of rocky
debris 1,640 feet long. It is
peanut-shaped. Astronomers have found
that Itokawa is like a giant space cushion, and very hard to destroy. They calculated Itokawa's age using specks
of asteroid dust that were scooped by the Japanese Hayabusa spacecraft and
brought back to Earth in 2010.
-
- Itokawa is almost as old as the solar
system itself. Itokawa has survived countless asteroid collisions over 4.2
billion long years.
-
- The scientists used a radioactive dating
method called argon-argon dating to measure Itokawa's age, which they clocked
at 4.2 billion years. They measured how
much the dust particles had been affected by shocks from asteroid collisions.
For this, the researchers used another method called electron backscatter
diffraction to measure the structures and orientations of crystals embedded
inside the dust particles.
-
- The team found that the dust particles were
mostly pristine, suggesting that they were excavated from deep within the
parent asteroid, likely when it broke apart during the catastrophic collision.
The scientists concluded that Itokawa is extremely resilient to collisions,
thanks to the asteroid's highly porous nature.
-
- Itokata hosts boulders of different shapes
and sizes that have blended under gravity. The rubble pile is entirely made of
loose boulders and rocks, with almost half of it being empty space.
-
- When asteroids impact Itokawa, large
cavities or pores between these boulders absorb much of the resulting energy
surge, protecting the asteroid's structure from fractures. In this way, the
pores help rubble piles like Itokawa survive asteroid collisions for at least
10 times longer than conventional, single-body asteroids, also known as
monoliths.
-
- Analysis of Itokawa suggests that thanks to
their resilience in the face of impacts, rubble-pile asteroids may be more
common, both in the asteroid belt and near-Earth.
-
- And the structure of an asteroid may make a
difference if humans need to choose a strategy for deflecting a threat. For
example, NASA's Double Asteroid Redirection Test (DART) mission rammed into
Dimorphos, a similar rubble pile that was not on a collision course with Earth,
but that was a convenient target to test how humans might respond to a future
threatening asteroid. The impact shortened Dimorphos' orbit around the larger
asteroid Didymos by 33 minutes, a major success for the mission.
-
- When it collided with Dimorphos, DART
transferred its energy and momentum to the asteroid. Although this kinetic
impact was successful with DART, it may
be less efficient at deflecting shock-absorbent porous asteroids.
-
- The kinetic impactor method is also most
effective when we spot asteroids on collision courses with Earth well in
advance, leaving enough time for a small change in orbit to build up.
-
- If a threatening asteroid is spotted too
late for the kinetic impactor approach, we can then potentially use a more
aggressive approach like using the shockwave of a close-by nuclear blast to
push a rubble-pile asteroid off course without destroying it.
-
- This is the stuff that movies re made
from.
-
January 30, 2022 ASTEROIDS
- threaten our planet? 3852
----------------------------------------------------------------------------------------
-----
Comments appreciated and Pass it on to whomever is interested. ---
--- Some
reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email
feedback, corrections, request for copies or Index of all reviews
---
to: ------ jamesdetrick@comcast.net ------
“Jim Detrick” -----------
--------------------- --- Monday, January 30, 2023 ---------------------------
-
No comments:
Post a Comment