- 2094 - Vesta
is the second most massive body in the asteroid belt, surpassed only by Ceres,
which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta
is occasionally visible from Earth with the naked eye. It is the first asteroid
to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011,
providing new insights into this rocky world.
-
-
-
-
----------------------------- 2094
- Vesta, second most massive asteroid
-
- Vesta
is the second most massive body in the asteroid belt, surpassed only by Ceres,
which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta
is occasionally visible from Earth with the naked eye. It is the first asteroid
to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011,
providing new insights into this rocky world.
-
- In 1596, while determining the elliptical
shape of planetary orbits, Johannes Kepler came to believe that a planet should
exist in the gap between Mars and Jupiter. Mathematical calculations made in
1772 seemed to support this prediction.
-
- In
August 1798, a German astronomer Heinrich Olbers discovered the second known
asteroid, Pallas. In a letter to a fellow
astronomer, he put forth the first theory of asteroid origin. He wrote, "Could
it be that Ceres and Pallas are just a pair of fragments of a once greater
planet which at one time occupied its proper place between Mars and
Jupiter?"
-
- Olbers reasoned that the fragments of such a
planet would intersect at the point of the explosion, and again in the orbit
directly opposite. He observed these two areas nightly, and on March 29, 1807 he discovered Vesta. After measuring several nights' worth of
observations, Olbers sent his calculations to mathematician Carl Friedrich
Gauss, who remarkably computed the orbit of Pallas in only 10 hours. As such,
he was given the honor of naming the new body. He chose the name Vesta, goddess
of the hearth, and sister to Ceres.
-
- Vesta is unique among asteroids in that it
has light and dark patches on the surface, much like the moon. Ground-based
observations determined that the asteroid has basaltic regions, meaning that
lava once flowed across its surface. It has an irregular shape, roughly that of
an oblate spheroid, a smooshed sphere.
-
------------------------------------- Diameter:
---------- 329 miles (530 kilometers)
-
-------------------------------------
Mass: : ------------- 5.886
X 1020 lbs. (2.67 x 1020 kilograms)
-
-------------------------------------
Temperature: : ----- 85 to 255 K (minus 306 to 0 Fahrenheit).
-
-------------------------------------
Albedo: ------------ 0.4322
-
-------------------------------------
Rotation period:------ 5.342 hours
-
-------------------------------------
Orbital period: ------ 3.63 years
-
-------------------------------------
Eccentricity: : ------ .0886
-
-------------------------------------
Aphelion: : --------- 2.57
AU
-
- ------------------------------------Perihelion:-------------
2.15 AU
-
------------------------------------ Closest to Earth: ------ 1.14 AU
-
- When Vesta made this close approach to Earth
in 1996, the Hubble Space Telescope mapped its topographic surface and
features. This revealed a large crater at the south pole that slices into its
interior. The crater averages 460 km in diameter.
-
- Vesta itself is only 530 km across. It cuts
an average of 13 km into the crust, and most likely formed from an impact in
the asteroid's early life. The material ejected from this collision resulted in
a number of smaller asteroids that orbit near their parent, as well as some of
the meteorites that have crashed into Earth.
-
- Unlike most asteroids, the interior of Vesta
is differentiated. Like the terrestrial
planets, the asteroid has a crust of cooled lava covering a rocky mantle and an
iron and nickel core. This lends credence to the argument for naming Vesta as a
protoplanet, rather than as an asteroid.
-
- Vesta's core accreted rapidly within the
first 10 million years after the formation of the solar system. The basaltic crust of Vesta also formed quickly, over the
course of a few million years. Volcanic eruptions on the surface stemmed from
the mantle, lasting anywhere from 8 to 60 hours. The lava flows themselves
ranged from a few hundred meters to several kilometers, with a thickness between
5 to 20 meters. The lava cooled rapidly, only to be buried again by more lava
until the crust was complete.
-
- Dawn's
gravity put its core at about 18 percent of Vesta's mass, or proportionally
about two-thirds as massive as Earth's core.
If it weren't for Jupiter, Vesta could have had a good chance at
becoming a planet.
-
- In 1960, a fireball streaking through the sky
over Millbillillie, Australia, announced the arrival of a piece of Vesta on Earth. Composed
almost entirely of pyroxene, a mineral found in lava flows, the meteorite bears
the same spectrometry analysis as Vesta.
-
- NASA's Dawn spacecraft visited the asteroid
in 2012 and discovered that the rocky body had a surprising amount of hydrogen on its surface. It
also found bright, reflective regions that may have been left over from its birth.
-
-
There is a massive mountain that towers over Vesta's southern pole. The
enormous mountain reaches up over 65,000 feet in height, making it nearly as
tall as Olympus Mons, the largest mountain ,and volcano, in the solar system.
Olympus Mons soars about 15 miles above the surface of Mars.
-
- The south polar mountain is larger than the
big island of Hawaii, the largest mountain on Earth, as measured from the ocean
floor. Liquid water once flowed across
the asteroid. Images captured by the Dawn spacecraft revealed curved gullies
and fan-shaped deposits within eight different Vesta impact craters. All eight
of the craters are thought to have formed within the last few hundred million
years, fairly recent in the lifetime of the 4.5-billion-year-old asteroid.
-
- Nobody expected to find evidence of water on
Vesta. The surface is very cold and there is no atmosphere, so any water on the
surface evaporates. The features could have been created by debris flows, as
opposed to pure water rivers or streams, that sculpted the Vesta gullies. Meteorites bombarding the asteroid melted ice
deposits beneath the surface, sending liquid water and small rocky particles
flowing down the crater walls. Such activity suggests the presence of ice buried beneath the surface.
-
- The craters with curved gullies are
associated with pitted terrain, which has been independently suggested as
evidence for loss of volatile gases from Vesta.
Ice could have been responsible for modifying Vesta's surface. In 2017,
a study suggested that smooth patches of terrain on the asteroid frequently
possessed high concentrations of hydrogen, which is often seen when solar radiation
breaks down water molecules.
-
- Modifications of the surface by melting of
buried ice could be responsible for smoothing those areas. Buried ice could have been brought to the
surface after an impact, which caused heated ice to melt and travel up through
the fractures to the surface.
-
- Dawn also observed signs of hydrated minerals
containing water molecules on Vesta's surface, which could also hint of the
presence of buried ice. The hydrated materials were associated with older
terrains, and could have been delivered by impacts of material from farther out in the
solar system.
-
- A low-altitude map of Vesta revealed a rich
geology. The steep slopes found on the asteroid, combined with its high
gravity, paves the way for rocks to roll downward, exposing other material.
Dawn revealed a variety of minerals, including some bright and dark materials
that could relate to potential buried ice.
- Vesta's unique composition means that it is
responsible for an entire group of meteorites. The HED meteorites, made up of
howardites, eucrites and diogenites, tell the story of Vesta's early life. Eucrites
form from hardened lava, while diogenites come from beneath the surface.
Howardites are a combination of the two, formed when a large impact mixed the
two sections together.
-
- Vesta has been suspected as being the source
of the HED meteorites since 1970. Dawn's mapping spectrometer verified that
proposition. The Dawn team thinks the HEDs came from an impact basin named
Rheasilvia, after an ancient Roman vestal virgin priestess. At 310 miles in
diameter, Rheasilvia is nearly as large as Vesta itself. It most likely formed
from a collision that stripped away most of the southern hemisphere's crust,
revealing the asteroid's interior.
-
- Vesta likely came close to shattering, the blow left concentric sets of troughs,
fracture lines around Vesta's equator. Parallel troughs may be another sign of
the enormous impact.
-
- In September 2007, NASA launched the Dawn mission, which is
unique in that it was the first craft to enter orbit around one solar system
body, then proceed to a second. Dawn entered orbit around Vesta in July 2011.
After studying the asteroid for a year, it left Vesta encountered Ceres
in March 2015.
-
- NASA's Dawn mission is to study the
characteristics of the early solar system by analyzing the two asteroids, which
are very different. Ceres is wet, with
seasonal polar caps, and may have a thin atmosphere. Vesta, on the other hand,
is dry and rocky. Studying the unique spectral signatures in its rocky crust
will expand our knowledge of our own planet, as well as Mars and Mercury.
-
- Given their size, the two are actually
regarded as protoplanets, or small planets. The gravitational pull of
Jupiter disrupted their formation. Without the presence of the gas giant, the
two may well have continued to evolve into full-size planets.
-
- We now know that Vesta is the only intact,
layered planetary building block surviving from the very earliest days of the
solar system. Dawn's study of Vesta
allowed for the creation of the best map to date of the asteroid. In October 2010, the Hubble Space Telescope
imaged Vesta again. The resulting data revealed that the
asteroid was tilted approximately four degrees more than scientists originally
thought. These findings helped NASA to place the spacecraft in the appropriate
polar orbit around the asteroid. Dawn requires light from the sun in order to
perform its mapping and imaging assignments.
-
- See Review 1618 to learn more about Vesta It includes information of how a gravity map
was used to map the concentrations of mass on the asteroid.
-
- See Review 847 about Ceres the 5th planet in
our solar system, now a protoplanet.
-
----------------------------------------------------------------------------------------
----- 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
------------------------- Sunday,
May 27, 2018
--------------------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment