Dead comets and near-earth encounters

October 13, 2015, Harvard-Smithsonian Center for Astrophysics
"Explore NEOs VIII: Dormant Short-Period Comets in the Near-Earth Asteroid Population," M. Mommert, A.W. Harris, M. Mueller, J.L. Hora, D.E. Trilling, W.F. Bottke, C.A. Thomas, M. Delbo, J.P. Emery, G. Fazio, and, H.A. Smith. An image of the asteroid Tempel 1 taken during the Deep Impact visit. Tempel 1 is about five kilometers across. CfA astronomers report that there are about one hundred large NEOs that are dormant, short-period comets, and about .3 - 3% of the fainter ones are too. Credit: NASA/JPL-Caltech/UMd

Near Earth Objects (NEOs) are asteroids or comets whose orbits sometimes bring them close to the Earth, thereby posing a potentially threat. The asteroid that struck Chelyabinsk last year was an NEO about 40 meters in diameter. While it is relatively easy to detect an NEO in visible light by watching its movement across the sky from night to night, determining its size and its potential hazard is more difficult because its optical brightness results from both its size and its reflectivity. CfA astronomers have for several years been using the IRAC infrared camera on Spitzer to measure the infrared light emitted by NEOs and, combined with optical measurements, to deduce their probable dimensions.

NEOs are thought to originate from collisional fragments of objects in the asteroid belt beyond the orbit of Mars, with over 10,000 known today. Short–period comets can also be NEOs, but unlike asteroids they most likely originated in the Kuiper belt, a reservoir of icy bodies outside the orbit of Neptune. The orbits of these bodies are disturbed as a result of gravitational perturbations with the giant planets, and some end up as NEOs, developing cometary tails when they approach the Sun and become active. After a while, their volatiles evaporate and these comets become dormant. As a result, it is very likely that the NEO population being studied includes a significant number of extinct comets.

CfA astronomers Joe Hora, Giovanni Fazio and Howard Smith and their colleagues reported two years ago on the discovery that the NEO Don Quixote is actually an extinct - they were able to find its faint cometary tail in . Now they and their colleagues have completed a statistical analysis of the full near infrared catalog of NEOs, searching for possible short-period comets by using a combination of their orbital parameters and their surface albedos as inferred from their near . The scientists found that between about 0.3 and 3% of the moderately bright NEOs are actually likely to be dormant, short-term period comets. They identify twenty-three specific ones as dormant comets. They also conclude that about one hundred large NEOs, with diameters larger than a kilometer. are probably also dormant short-period comets.

Explore further: The properties of a six-meter near-Earth object

More information: "Explore NEOs VIII: Dormant Short-Period Comets in the Near-Earth Asteroid Population," M. Mommert, A.W. Harris, M. Mueller, J.L. Hora, D.E. Trilling, W.F. Bottke, C.A. Thomas, M. Delbo, J.P. Emery, G. Fazio, and, H.A. Smith. arxiv.org/abs/1508.04116

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Returners
1.7 / 5 (6) Oct 13, 2015
The Sun is made of water, people.

Think about it. The oort Cloud, and the KBO's are mostly water.

All this stuff was pushed away as the Sun gave it's first light, but before the first light? Water.

The elemental composition of stars is guestimated based on the surface composition. Scientists know next to nothing about what goes on inside stars.

However, look around....all the stuff in the solar system is made of water and metals.

Who honestly thinks the Sun, the most massive object in the system, housing some 99% of the total mass, would be made of the lightest materials at the center of gravity? That's not how elements behave. Heavy elements sink first.

The Sun is made from Water and some metals. It's core is probably mostly Oxygen (from disassociated water,) which is one of the most abundant elements in any of the planets.

The Standard model is wrong.
Vietvet
4.3 / 5 (6) Oct 13, 2015
You're sick, get help.
wduckss
3 / 5 (4) Oct 14, 2015
Returners telling jokes (if it passes, it is good ..).
High temperatures decompose more complicated elements in hydrogen and helium (other elements, in trace). When temperatures melt the crust body stays hot "water." Saturn is lighter than water.
my2cts
3.8 / 5 (10) Oct 14, 2015
You're sick, get help.

I agree. Returners, you are flooding this blog at an alarming rate
and strictly everything you say is nonsense.
You have become unstable.
SuperThunder
2 / 5 (4) Oct 17, 2015
The Sun is made of water, people.


This is the greatest thing I've ever read in these comments. People 5000 years ago who only believed in four elements would be amazed by this assertion.

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