During winter in the polar regions, a thin layer of carbon dioxide ice covers the surface and then sublimates – turns directly from ice into vapour – with the first light of spring. In the dune fields, this springtime defrosting occurs from the bottom up, trapping gas between the ice and the sand. As the ice cracks, this gas is released violently and carries sand with it, forming the dark patches and streaks observed in this CaSSIS image. ESA/Roscosmos/CaSSIS, CC BY-SA 3.0 IGO
Springtime on Earth can be a riotous affair, as plants come back to life and creatures large and small get ready to mate. Nothing like that happens on Mars, of course. But even on a cold world like Mars, springtime brings changes, though you have to look a little more closely to see them.
Lucky for us, there are spacecraft orbiting Mars with high-resolution cameras, and we can track the onset of Martian springtime through images.
Dust-covered, boulder-strewn landscape on the smaller of the two lobes of Comet 67P/Churyumov-Gerasimenko taken from a distance of 5 miles (8 km). Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
We’ve subsisted for months on morsels of information coming from ESA’s mission to Comet 67P/Churyumov-Gerasimenko. Now, a series of scientific papers in journal Science offers a much more complete, if preliminary, look at Rosetta’s comet. And what a wonderful and complex world it is.
Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko’s nucleus according to terrain and named for Egyptian deities like Imhotep, Aten and Hathor. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA
Each of the papers describes a different aspect of the comet from the size and density of dust particles jetting from the nucleus, organic materials found on its surface and the diverse geology of its bizarre landscapes. Surprises include finding no firm evidence yet of ice on the comet’s nucleus. There’s no question water and other ices compose much of 67P’s 10 billion ton mass, but much of it’s buried under a thick layer of dust.
Despite its solid appearance, 67P is highly porous with a density similar to wood or cork and orbited by a cloud of approximately 100,000 “grains” of material larger than 2 inches (5 cm) across stranded there after the comet’s previous perihelion passage. Thousands of tiny comet-lets! Continue reading “Latest Research Reveals a Bizarre and Vibrant Rosetta’s Comet”
Comet Lovejoy re-emerging from behind the Sun on Dec. 15, 2011. (NASA/SDO)
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It was just about three months ago that the astronomy world watched in awe as the recently-discovered comet Lovejoy plummeted toward the Sun on what was expected to be its final voyage, only to reappear on the other side seemingly unscathed! Surviving its solar visit, Lovejoy headed back out into the solar system, displaying a brand-new tail for skywatchers in southern parts of the world (and for a few select viewers above the world as well.)
How did a loosely-packed ball of ice and rock manage to withstand such a close pass through the Sun’s blazing corona, when all expectations were that it would disintegrate and fizzle away? A few researchers from Germany have an idea.
Scientists from the Max Planck Institute for Extraterrestrial Physics and the Braunschweig University of Technology have hypothesized that Comet Lovejoy managed to hold itself together through the very process that, to most people, defines a comet: the outgassing of sublimated icy material.
As a comet near the Sun, the increased heating from solar radiation causes the frozen materials within the nucleus to sublimate — go directly and suddenly from solid to gas, skipping the liquid middle stage — and, in doing so, burst through the surface of the comet and create the long, hazy reflective tail that is so often associated with them.
Overview of the forces acting on sungrazing comets. (Illustration from paper.)
In the case of Lovejoy, which was on a direct path toward the Sun, the sublimation itself may have provided enough outward force across its surface to literally keep it together, according to the team’s research.
“The reaction force caused by the strong outgassing (sublimation) of the nucleus near the Sun acts to keep the nucleus together and to overcome the tidal disruption,” the paper claims.
In addition, the team states that the size of the comet’s nucleus can be derived using an equation that takes into consideration the combined forces of outgassing, the material composition of the comet’s nucleus, the comet’s own gravity and the tidal forces exerted by the comet’s close proximity to the Sun (i.e., the Roche limit).
Using that equation, the team concluded that the diameter of Comet Lovejoy’s nucleus is anywhere between 0.2 km and 11 km (.125 miles and 6.8 miles). Any smaller and it would have lost too much material during its pass (and had too little gravity); any larger and it would have been too thick for outgassing to provide enough counterbalancing force.
If this hypothesis is correct, taking a trip around the Sun may not mean the end for all comets… at least not those of a certain size!
Watch the video of Lovejoy’s Dec. 15 solar swing below:
The paper was submitted to the journal Icarus on March 8, 2012 by Bastian Gundlach. See the full text here.
