NEAR Mission Profile

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NEAR Shoemaker
at EROS
Debra Buczkowski Johns Hopkins Applied Physics Lab
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Background Questions

• What is an asteroid?
• Why go to an asteroid?
• What asteroids have we been to?
• Why go to Eros?
• What did we find?
• What have we learned?
• Outstanding questions

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What is an asteroid?

• Asteroids are a multitude of minor planets
  orbiting the Sun at distances ranging from inside
  Earths orbit to beyond Saturns

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What is an asteroid?

• Asteroids are a multitude of minor planets
  orbiting the Sun at distances ranging from inside
  Earths orbit to beyond Saturns
• Planetesimals gravitationally perturbed into
  tilted, elongated orbits and so collided and
  fragmented instead of accumulating into a larger
  body
• Primordial material

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What is an asteroid?

• Asteroids are a multitude of minor planets
  orbiting the Sun at distances ranging from inside
  Earths orbit to beyond Saturns
• Planetesimals gravitationally perturbed into
  tilted, elongated orbits and so collided and
  fragmented instead of accumulating into a single
  whole
• Primordial Material
• Families of asteroids
• Trojans, Atens, Apollos, Amors

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Why go to an asteroid?

• Structure of Asteroids
• Solid body vs. rubble pile
• S-type conundrum
• Types of meteorites
• Stone, Iron and Stony-Iron

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Why go to an asteroid?

• Composition of Asteroids
• Solid body vs. rubble pile
• S-type conundrum
• Types of meteorites
• Stone, Iron and Stony-Iron
• Ordinary Chondrites (Stone) are most common
• Types of asteroids
• 78 C-type (carbon rich) carbonaceous chondrites

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Why go to an asteroid?

• Are there main-belt parent bodies for the
  abundant ordinary chondrite meteorites?
• S-type asteroids could be space-weathered
  chondrites
• Density of asteroid
• Stony-iron object 5 g/cm3
• Ordinary chondrite 3.5 g/cm3
• Rubble pile densities even less
• Spectroscopy

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What asteroids have we been to?

• 951 Gaspra
• Galileo October 29, 1991

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What asteroids have we been to?

• 951 Gaspra
• Galileo October 29, 1991
• 243 Ida
• Galileo August 28, 1993

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What asteroids have we been to?

• 951 Gaspra
• Galileo October 29, 1991
• 243 Ida
• Galileo August 28, 1993
• 253 Mathilde
• NEAR June 27, 1997

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What asteroids have we been to?

• 951 Gaspra
• Galileo October 29, 1991
• 243 Ida
• Galileo August 28, 1993
• 253 Mathilde
• NEAR June 27, 1997
• 433 Eros
• 25143 Itokawa

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Public Release Image courtesy of the Japanese
Space Agency
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Why go to Eros?

• First discovered and second largest near-Earth
  asteroid
• Eros is an Amor (an Earth-approaching asteroid)

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Why go to Eros?

• First discovered and second largest near-Earth
  asteroid
• Eros is an Amor (an Earth-approaching asteroid)
• More than a century of ground-based studies
• Repeated close encounters with Earth
• Gravity strong enough to hold a spacecraft in
  orbit
• Eros is a S-type asteroid

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NEAR Shoemaker

• The first Discovery mission

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NEAR Shoemaker

• The first Discovery mission
• Simplicity and low cost were the main principles
• Managed by the Applied Physics Laboratory
• Five instruments in the science payload
• Multispectral imager (MSI)
• Near-infrared spectrometer (NIS)
• X-ray/gamma-ray spectrometer (XGRS)
• NEAR laser rangefinder (NLR)
• Magnetometer (MAG)
• Radio science (RS)

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NEAR Shoemaker Timeline

• Launched February 17, 1996
• Mathilde flyby June 27, 1997
• Lost contact December 20, 1998
• Orbit around Eros February 14, 2000
• Touchdown on Eros February 12, 2001

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What did Near find?

• Radio Science
• Density of interior is nearly uniform
• Consistent with a consolidated body
• Magnetometer
• No magnetic field
• NEAR Laser Rangefinder

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What did Near find?

• Radio Science
• Density of interior is nearly uniform
• Consistent with ordinary chondrites
• Magnetometer
• No magnetic field
• NEAR Laser Rangefinder
• X-ray/Gamma-ray Spectrometer
• Composition comparable to ordinary chondrites
• Near-infrared Spectrometer
• Olivine and pyroxene similar to ordinary
  chondrites

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What did Near find?

• Multispectral Imager
• More than 160, 000 images

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What did Near find?

• Multispectral Imager
• More than 160, 000 images
• Craters
• Grooves and ridges
• Boulders
• Regolith
• Aided in the creation of the Eros shape model
• Allowed mapping of Eros

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Tutanekai
Jahan
Mahal
Psyche
Eurydice
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What have we learned? NEAR Mission Findings

• Bulk elemental composition consistent with
  ordinary chondrites
• Mg, Si, Al, Fe, Ca emissions, but sulfur levels
  are low
• Not a rubble pile
• grooves, crater chains, and ridges trending
  east-west, suggestive of underlying strata or
  faults
• Uniform density throughout
• Regolith
• No magnetic field

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Outstanding Questions

• Why is the sulfur level low?
• How consolidated or fractured is Eros?
• What caused the ponds?
• Why is Eros so non-magnetic?

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