Starship Asterisk*

orin stepanek wrote:Some of the craters remind me of something that was bubbling hot and suddenly cooled down. I would think there should have been some frozen dome structures if that were the case though.

ZenGrouch wrote:
How are the north and south poles determined on asteroids?

http://en.wikipedia.org/wiki/Poles_of_astronomical_bodies wrote:
<<The International Astronomical Union (IAU) defines the geographic north pole of a planet or any of its satellites in the solar system as the planetary pole that is in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North pole. This definition means that an object's direction of rotation may be negative (retrograde rotation) — in other words, it rotates clockwise when viewed from above its north pole, rather than the "normal" counterclockwise direction exhibited by Earth's north pole. Venus rotates in the opposite direction to the other planets, and Uranus has been knocked on its side and rotates almost perpendicular to the rest of the solar system. The ecliptic remains within 3° of the invariable plane over five million years, but is now inclined about 23.44° to Earth's celestial equator used for the coordinates of poles. This large inclination means that the declination of a pole relative to Earth's celestial equator could be negative even though a planet's north pole (such as Uranus) is north of the invariable plane.

In 2009 the responsible IAU Working Group decided to define the poles of dwarf planets, minor planets, their satellites, and comets according to the right-hand rule. To avoid confusion with the "north" and "south" definitions relative to the invariable plane, "positive" is the pole toward which the thumb points when the fingers are curled in its direction of rotation ("negative" for the opposite pole). This change was needed because the poles of some asteroids and comets precess rapidly enough for their north and south poles to swap within a few decades using the invariable plane definition.

The projection of a planet's geographic north pole onto the celestial sphere gives its north celestial pole. The coordinates are given relatve to Earth's celestial equator and the vernal equinox as they existed at J2000 (2000 January 1 12:00:00 TT) which is a plane fixed in inertial space now called the International Celestial Reference Frame (ICRF). Many poles precess or otherwise move relative to the ICRF, so their coordinates will change. Some bodies in the solar system, including Saturn's moon Hyperion and the asteroid 4179 Toutatis, lack a stable geographic north pole. They rotate chaotically because of their irregular shape and gravitational influences from nearby planets and moons, and as a result the instantaneous pole wanders over their surface, and may momentarily vanish altogether (when the object comes to a standstill with respect to the distant stars).>>

Ann wrote:
Is this weird south polar feature the same thing as the famous "nose" of Vesta?

o.b.zervar wrote:when an iron based object is struck hard enough to liquefy the crust the electro-magnetic field,combined with the air flow vectors and subsequent loss of heat,willl determine the form of the coagulating sructure. this shot shows the result of a polar region impact.

neufer wrote:

Ann wrote:
Is this weird south polar feature the same thing as the famous "nose" of Vesta?

More like the Grand Teton of [Rheasilvia].

http://en.wikipedia.org/wiki/Rhea_Silvia wrote:

Rhea Silvia, torso from the amphitheatre at Cartagena in Spain.

<<Rhea Silvia (also written as Rea Silvia), and also known as Ilia, was the mythical mother of the twins Romulus and Remus, who founded the city of Rome. Her story is told in the first book of Ab Urbe Condita of Livy. According to Livy she was the daughter of Numitor, king of Alba Longa, and descended from Aeneas. Numitor's younger brother Amulius seized the throne and killed Numitor's son, then forced Rhea Silvia to become a Vestal Virgin, a priestess of the goddess Vesta. As Vestal Virgins were sworn to celibacy for a period of thirty years, this would ensure the line of Numitor had no heirs.

However, Rhea Silvia conceived and gave birth to the twins Romulus and Remus, claiming that the god Mars had discovered her in the forest and seduced her.

When Amulius learned of the birth he imprisoned Rhea Silvia and ordered a servant to kill the twins. But the servant showed mercy and set them adrift on the river Tiber, which, overflowing, left the infants in a pool by the bank. There a she-wolf (Lupa), who had just lost her own cubs suckled them. Subsequently Faustulus rescued the boys. Romulus and Remus went on to found Rome, overthrow Amulius, and reinstate Numitor as King of Alba Longa.

In a version presented by Ovid, it is the river Anio who takes pity on her and invites her to rule in his realm. The name Rhea Silvia suggests a minor deity, a demi-goddess of forests. Silva means woods or forest, and Rea may be related to res and regnum; Rea may also be related to Greek rheô, "flow," and thus relate to her association with the spirit of the river Tiber. Carsten Niebuhr proposed that the name Rhea Silvia came from Rea, meaning guilty, and Silvia meaning of the forest and so assumed that Rhea Silvia was a generic name for the guilty woman of the forest, i.e. the woman who had been seduced there.>>

http://www.universetoday.com/89093/rhea-silvia-super-mysterious-south-pole-basin-at-vesta-is-named-after-romulus-and-remus-roman-mother/#more-89093 wrote:
Rheasilvia – Super Mysterious South Pole Basin at Vesta is Named after Romulus and Remus Roman Mother
by Ken Kremer on September 21, 2011

A False-Color Topography of Vesta's South Pole dominated by Rheasilvia This false-color map of the giant asteroid Vesta was created from stereo images obtained by the framing camera aboard NASA’s Dawn spacecraft. The terrain model of Vesta's southern hemisphere shows a big circular structure - Rheasilvia - with a diameter of about 500 kilometers, its rim rising above the interior of the structure for more than 15 km. [The central] mountain, which measures about 200 km in diameter at its base, is one of the highest elevations on all known bodies with solid surfaces in the solar system. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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<<‘Rheasilvia’ – that’s the brand new name given to the humongous and ever more mysterious South Pole basin feature being scrutinized in detail by Dawn, according to the missions top scientists in a Universe Today exclusive. What is Rheasilvia? An impact basin? A crater remnant? Tectonic action? A leftover from internal processes? Or something completely different? That’s the hotly debated central question consuming loads of attention and sparking significant speculation amongst Dawn’s happily puzzled international science team. There is nothing closely analogous to Vesta and Rhea Silvia – and thats a planetary scientists dream come true.

“Rheasilvia – One thing that we all agree on is that the large crater should be named ‘Rheasilvia’ after the mother of Romulus and Remus, the mythical mother of the Vestals,” said Prof. Chris Russell, Dawn's lead scientist, in an exclusive interview with Universe Today.

Prior to Dawn’s orbital insertion in July 2011, the best views of Vesta were captured by the Hubble Space Telescope and clearly showed it wasn’t round. Scientists interpreted the data as showing that Vesta’s southern hemisphere lacked a South Pole! And, that it had been blasted away eons ago by a gargantuan cosmic collision that excavated huge amounts of material that nearly utterly destroyed the asteroid. “We are trying to understand the high scarps that we see and the scarps that should be there and aren’t,” Russell explained. “We are trying to understand the landslides we think we see and why the land slid. We see grooves in the floor of the basin and want to interpret them. “And the hill in the center of the crater remains as mysterious today as when we first arrived.”

Another top Dawn scientist described Rheasilvia in this way: “I would say that the floor of the impact feature contains chaotic terrain with multiple sets of intersecting grooves, sometimes fairly straight and often curvy, said Carol Raymond to Universe Today. Raymond is Dawn’s Deputy Principal Investigator from NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

“The crater rim is not well-expressed”, Raymond told me. “We see strong color variations across Vesta, and the south pole impact basin appears to have a distinct spectral signature. The analysis is still ongoing,” Russell said. “The south is distinctly different than the north. The north has a varied spectrum and the south has a distinct spectral feature but it has little variation.” Time will tell as additional high resolution measurements are collected from the forthcoming science campaign at lower orbits.

Russell further informed that the team is rushing to pull all the currently available data together in time for a science conference and public briefing in mid-October. “We have set ourselves a target to gather everything we know about the south pole impact feature and expect to have a press release from what ever we conclude at the GSA (Geological Society of America) meeting on October 12. “We will tell the public what the options are. We do not have a good analog to Vesta anywhere else in the Solar System and we’ll be studying it very intently.”

Right now Dawn is using its ion propulsion system to spiral down four times closer to Vesta, as it descends from the initlal survey orbit (about 2700 km) to the new science orbit, elegantly named HAMO – or High Altitude Mapping Orbit (about 685 km.)>>

http://dawn.jpl.nasa.gov/multimedia/imageoftheday/image.asp?date=20110927 wrote:

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3-D Image of Grooves and Wrinkles in the South Polar Region
September 27, 2011

PASADENA, Calif. -- NASA's Dawn spacecraft obtained this 3-D image of Vesta with its framing camera on Aug. 23 and 28, 2011. This image of the south polar region was taken through the camera's clear filter at a distance of 1,700 miles. The image has a resolution of about 260 meters per pixel.