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posted by martyb on Friday October 20 2017, @09:33AM   Printer-friendly
from the Tony-Orlando-would-be-pleased dept.

The Dawn spacecraft will continue to orbit the dwarf planet Ceres, and will capture closer imagery than ever before:

NASA has authorized a second extension of the Dawn mission at Ceres, the largest object in the asteroid belt between Mars and Jupiter. During this extension, the spacecraft will descend to lower altitudes than ever before at the dwarf planet, which it has been orbiting since March 2015. The spacecraft will continue at Ceres for the remainder of its science investigation and will remain in a stable orbit indefinitely after its hydrazine fuel runs out.

The Dawn flight team is studying ways to maneuver Dawn into a new elliptical orbit, which may take the spacecraft to less than 120 miles (200 kilometers) from the surface of Ceres at closest approach. Previously, Dawn's lowest altitude was 240 miles (385 kilometers).

[...] The extended mission at Ceres additionally allows Dawn to be in orbit while the dwarf planet goes through perihelion, its closest approach to the Sun, which will occur in April 2018. At closer proximity to the Sun, more ice on Ceres' surface may turn to water vapor, which may in turn contribute to the weak transient atmosphere detected by the European Space Agency's Herschel Space Observatory before Dawn's arrival. Building on Dawn's findings, the team has hypothesized that water vapor may be produced in part from energetic particles from the Sun interacting with ice in Ceres' shallow surface. Scientists will combine data from ground-based observatories with Dawn's observations to further study these phenomena as Ceres approaches perihelion.

The Dawn spacecraft will remain in orbit at Ceres, where it is expected to operate until late 2018, without being crashed into the surface or sent to another target.


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Ceres May Have Had a Global Surface Ocean in the Past 14 comments

Dawn Finds Possible Ancient Ocean Remnants at Ceres

Minerals containing water are widespread on Ceres, suggesting the dwarf planet may have had a global ocean in the past. What became of that ocean? Could Ceres still have liquid today? Two new studies from NASA's Dawn mission shed light on these questions.

The Dawn team found that Ceres' crust is a mixture of ice, salts and hydrated materials that were subjected to past and possibly recent geologic activity, and that this crust represents most of that ancient ocean. The second study builds off the first and suggests there is a softer, easily deformable layer beneath Ceres' rigid surface crust, which could be the signature of residual liquid left over from the ocean, too.

"More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground," said Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Ceres.

Constraints on Ceres' internal structure and evolution from its shape and gravity measured by the Dawn spacecraft (open, DOI: 10.1002/2017JE005302) (DX)

The interior structure of Ceres as revealed by surface topography (DOI: 10.1016/j.epsl.2017.07.053) (DX)

Previously: Dawn Spies Magnesium Sulphate and Possible Geological Activity on Ceres
Ceres's Cryovolcanoes Viscously Relax Into Nothingness
Organic Molecules Found on Ceres
Early Asteroids May Have Been Made of Mud Rather Than Rock
Dawn Mission Extended at Ceres


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Bright Areas on Ceres Suggest Geologic Activity 8 comments

Bright Areas on Ceres Suggest Geologic Activity

Since Dawn arrived in orbit at Ceres in March 2015, scientists have located more than 300 bright areas on Ceres. A new study in the journal Icarus, led by Nathan Stein, a doctoral researcher at Caltech in Pasadena, California, divides Ceres' features into four categories.

The first group of bright spots contains the most reflective material on Ceres, which is found on crater floors. The most iconic examples are in Occator Crater, which hosts two prominent bright areas. Cerealia Facula, in the center of the crater, consists of bright material covering a 6-mile-wide (10-kilometer-wide) pit, within which sits a small dome. East of the center is a collection of slightly less reflective and more diffuse features called Vinalia Faculae. All the bright material in Occator Crater is made of salt-rich material, which was likely once mixed in water. Although Cerealia Facula is the brightest area on all of Ceres, it would resemble dirty snow to the human eye.

More commonly, in the second category, bright material is found on the rims of craters, streaking down toward the floors. Impacting bodies likely exposed bright material that was already in the subsurface or had formed in a previous impact event.

Separately, in the third category, bright material can be found in the material ejected when craters were formed.

The mountain Ahuna Mons gets its own fourth category -- the one instance on Ceres where bright material is unaffiliated with any impact crater. This likely cryovolcano, a volcano formed by the gradual accumulation of thick, slowly flowing icy materials, has prominent bright streaks on its flanks.

Ceres and cryovolcanos.

The formation and evolution of bright spots on Ceres (open, DOI: 10.1016/j.icarus.2017.10.014) (DX)

Previously: A Closer Look At Mystery Spots On Dwarf Planet Ceres
NASA's Dawn Orbiter Finds a Mountain on Ceres
Ceres's Cryovolcanoes Viscously Relax Into Nothingness
Organic Molecules Found on Ceres
Dawn Mission Extended at Ceres
Ceres May Have Had a Global Surface Ocean in the Past


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Dawn's Orbit Around Ceres: A New Low 9 comments

Previously, NASA planned to lower the closest approach to Ceres of the Dawn spacecraft to around 120 miles (200 km) from 239 miles (385 km). Now, the XMO7 orbit will reach an altitude of just 22 miles (35 km) above Ceres. The images returned should be over 9000 times better than what Hubble can capture. This is the final orbit planned:

NASA's Dawn spacecraft is maneuvering to its lowest-ever orbit for a close-up examination of the inner solar system's only dwarf planet.

In early June, Dawn will reach its new, final orbit above Ceres. Soon after, it will begin collecting images and other science data from an unprecedented vantage point. This orbit will be less than 30 miles (50 kilometers) above the surface of Ceres -- 10 times closer than the spacecraft has ever been.

Dawn will collect gamma ray and neutron spectra, which help scientists understand variations in the chemical makeup of Ceres' uppermost layer. That very low orbit also will garner some of Dawn's closest images yet.

The transfer from Dawn's previous orbit to its final one is not as simple as making a lane change. Dawn's operations team worked for months to plot the course for this second extended mission of the veteran spacecraft, which is propelled by an ion engine. Engineers mapped out more than 45,000 possible trajectories before devising a plan that will allow the best science observations.

Previously: Dawn Mission Extended at Ceres

Related: Ceres May Have Had a Global Surface Ocean in the Past
Evidence of a Seasonal Water Cycle and Surface Changes Found on Ceres


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Dawn's Orbit Around Ceres: First Images 3 comments

The Dawn spacecraft has entered its lowest-ever orbit around Ceres:

Dawn entered orbit around 1 Ceres on March 6, 2015. Up until this year, Dawn's orbits brought it no closer than 483 kilometers (300 miles) from the rock's surface. The complicated process of entering the new 27-hour, 13-minute orbit around the asteroid began on April 16th, when NASA engineers instructed Dawn to fire its ion engines. The new orbit has a periapsis of less than 48 km above the pockmarked surface of Ceres and an apoapsis of 4,000 km.

[...] Attaining a low orbit around Ceres object is no mean feat, as the asteroid's gravitational field is lumpy due to the asteroid's uneven composition. NASA engineers looked at over 45,000 possible trajectories before settling on the solution. A lower orbit will allow researchers to map Ceres's gravitational field and hence its internal mass distribution. Surprises may be in store, though: Dawn's reaction wheels failed earlier this year, so it now uses its hydrazine-fueled thrusters to control its orientation in space.

[...] We can enjoy the final closeups of Ceres before Dawn falls silent later this year. Then, the excitement in asteroid exploration will shift towards the arrival of the Japanese Aerospace Exploration Agency's Hayabusa-2 at 162173 Ryugu this July, as well as Osiris-REX's arrival at 101955 Bennu this August.

Check out Landslides Along Occator Crater's Rim and other recent images.

162173 Ryugu and 101955 Bennu.

Previously: Dawn Mission Extended at Ceres
Dawn's Orbit Around Ceres: A New Low

Related: Ceres May Have Had a Global Surface Ocean in the Past
Evidence of a Seasonal Water Cycle and Surface Changes Found on Ceres


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Dawn Spacecraft Runs Out of Hydrazine, Ceases Operations 13 comments

NASA's Dawn Mission to Asteroid Belt Comes to End

NASA's Dawn spacecraft has gone silent, ending a historic mission that studied time capsules from the solar system's earliest chapter.

Dawn missed scheduled communications sessions with NASA's Deep Space Network on Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its pointing. Dawn can no longer keep its antennae trained on Earth to communicate with mission control or turn its solar panels to the Sun to recharge.

The Dawn spacecraft launched 11 years ago to visit the two largest objects in the main asteroid belt. Currently, it's in orbit around the dwarf planet Ceres, where it will remain for decades.

Ceres, Vesta, and Dawn.

Also at Ars Technica, The Verge, and Science News.

Previously: NASA's Dawn Spacecraft Nears the End of its Mission
NASA Retires the Kepler Space Telescope after It Runs Out of Hydrazine

Related:


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