-
-
----------------------------- 2203 - Asteroid Bennu
-
- On December 3, 2018, after traveling billions of miles from Earth, NASA's spacecraft reached its target, the asteroid Bennu. The spacecraft started a nearly two-year, up-close investigation of this near-earth asteroid. It will inspect nearly every square inch of this ancient clump of rubble left over from the formation of our solar system. The spacecraft will pick up a sample of pebbles and dust from Bennu's surface and deliver it back to Earth in 2023.
-
- Generations of planetary scientists will get to study pieces of the primitive materials that formed our planetary system. We will better understand the role asteroids may have played in delivering life-forming compounds to our planets and moons.
-
- It is not just history that the mission to Bennu will help uncover. Scientists studying the rock through instruments in space will also shape our future. As the instruments collect the most detailed information yet about the forces that move asteroids, experts will improve their predictions of which asteroids could be on a crash course with our planet in the future.
-
- About a third of a mile wide, Bennu is large enough to reach Earth's surface. Many smaller space objects would burn up in our atmosphere. If it impacted Earth, Bennu is big enough to cause widespread damage. It could wipe out the dinosaurs that are still here.
-
- Bennu will come close enough to Earth over the next century to pose a 1 in 2,700 chance of impacting it between 2175 and 2196. Those odds mean there is a 99.963 percent chance the asteroid will miss the Earth. Astronomers want to know exactly where Bennu is located at all times. Just in case something changes.
-
- Astronomers have estimated Bennu's future trajectory after observing it several times since it was discovered in 1999. They have turned their optical, infrared and radio telescopes toward the asteroid every time it came close enough to Earth, about every six years, to deduce features such as its shape, rotation rate and trajectory.
-
- Scientists have estimated Bennu's trajectory around the Sun far into the future. Their predictions are informed by ground observations and mathematical calculations that account for the gravitational nudging of Bennu by the Sun, the Moon, planets and other asteroids, plus non-gravitational factors like the Yarkovsky effect.
-
- Given these parameters, astronomers can predict the next four exact dates in September of 2054, 2060, 2080 and 2135 that Bennu will come within 5 million miles of Earth. That's close enough that Earth's gravity will slightly bend Bennu's orbital path as it passes by. As a result, the uncertainty about where the asteroid will be each time it loops back around the Sun will grow, causing predictions about Bennu's future orbit to become increasingly hazy after 2060. December 11 every six years is a date to watch out for.
-
- In 2060, Bennu will pass Earth at about twice the distance from here to the Moon. But it could pass at any point in a 19 mile window of space. A very small difference in position within that window will get magnified enormously in future orbits and make it increasingly hard to predict Bennu's trajectory.
-
- When this asteroid comes back near Earth in 2080 the best window we can get on its whereabouts is nearly 9,000 miles wide. By 2135, when Bennu's shifted orbit is expected to bring it closer than the Moon, its flyby window grows wider, to nearly 100,000 miles. This will be Bennu's closest approach to Earth over the five centuries for which we have reliable calculations.
-
- There's another phenomenon nudging Bennu's orbit and muddying future impact projections. It's called the Yarkovsky effect. Having nothing to do with gravity, the Yarkovsky effect alters Bennu's orbit because of heat from the Sun.
-
- There are a lot of factors that might affect the predictability of Bennu's trajectory in the future, but most of them are relatively small. The one that's most sizeable is this Yarkovsky effect.
-
- This heat nudge was named after the Polish civil engineer who first described it in 1901: Ivan Osipovich Yarkovsky. He suggested that sunlight warms one side of a small, dark asteroid and some hours later radiates that heat away as the asteroid rotates its hot side into cold darkness. This thrusts the rock pile a bit, either toward the Sun or away from it, depending on the direction of its rotation.
-
- In Bennu's case, astronomers have calculated that the Yarkovsky effect has shifted its orbit about 0.18 miles per year toward the Sun since 1999. In fact, it helped deliver Bennu to our part of the solar system, in the first place, from the asteroid belt between Mars and Jupiter over billions of years. Now, Yarkovsky is complicating our efforts to make predictions about Bennu's path relative to Earth.
-
- The spacecraft will transmit radio tracking signals and capture optical images of Bennu that will help NASA scientists determine its precise position in the solar system and its exact orbital path. Combined with existing, ground-based observations, the space measurements will help clarify how Bennu's orbit is changing over time.
-
- Additionally, astronomers will get to test their understanding of the Yarkvovksy effect on a real-life asteroid for the first time. They will instruct the spacecraft to follow Bennu in its orbit about the Sun for about two years to see whether it's moving along an expected path based on gravity and Yarkovsky theories. Any differences between the predictions and reality could be used to refine models of the Yarkovsky effect.
-
- Even more significant to understanding Yarkovsky better will be the thermal measurements of Bennu. During its mission the spacecraft will track how much solar heat radiates off the asteroid, and where on the surface it's coming from data that will help confirm and refine calculations of the Yarkovsky effect on asteroids.
-
- The spacecraft also will address some open questions about the Yarkovsky theory. One of theory is how do boulders and craters on the surface of an asteroid change the way photons scatter off of it as it cools, carrying away momentum from the hotter side and thereby nudging the asteroid in the opposite direction? The measurements will help scientists understand this by mapping the rockiness of Bennu's surface.
-
- This mission is an amazing laboratory in space. What we learn may prevent an Earth- asteroid collision in the future. It will come by every six years to celebrate my brother’s birthday.
-
- Other Reviews available about asteroids:
- 1923 - Mission to visit Bennu. January 23, 2017, an asteroid 39 feet in diameter flew past Earth within 46,603 miles. In 2017 50 asteroids flew past at distances closer than the moon, which is 238,855 miles away
-
- 2044 - Oumuamua, the needle shaped asteroid. This asteroid came from outside our solar system and is on its way back into space.
-
- This Review 2044 lists an appendix of 15 other reviews about asteroids. Including:
-
- 1825 - Asteroids responsible for evolution on Earth?
-
- 1296 - When an asteroid hit Manson, Iowa.
-
- December 10, 2018
----------------------------------------------------------------------------------------
--- 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” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
-------------------------- Monday, December 10, 2018 --------------------------
------------------------------------------------------------------------------------------
No comments:
Post a Comment