Download COS Dec.3-2010-short-1 - UCF Physics

Detection of Water ice and Organic
Molecules on Asteroids
Humberto Campins
- University of Central Florida
- Instituto Astrofísica de Canarias, Spain
- Observatoire de la Côte d’Azur, France
UCF College of Science
Dec. 3, 2010
Ice and Organics on Asteroids:
24 Themis & 65 Cybele
Accepted Sept. 9, 2010
Outline
I.
Asteroids and the Early Solar System
II. Detection of Water-Ice and Organic
Molecules on 24 Themis & 65 Cybele
III. Implications on Origin of Earth’s Water &
Life
IV. Conclusions
V. Conclusions
 Water-ice and organic molecules detected on two
asteroids so far: 24 Themis and 65 Cybele
 Water more abundant on asteroids than expected
 Supports proposed asteroidal origin of Earth’s
water and organic molecules
 Helps understand origin and evolution of life on
Earth and possibility of Earth-like planets around
other stars
 Helps case for NASA’s OSIRIS-Rex mission
I. Asteroids and the Early Solar System
•
•
•
Planets, asteroids & comets formed from Solar
Nebula 4.6 billon years ago
Planets were transformed extensively
Asteroids & comets are “cosmic fossils” preserving
clues about early solar system
 Asteroids and
comets accreted at
different distances
from the Sun
Asteroids: more
rock
 Comets: more ice
Asteroid Belt
Asteroid Belt
24 Themis
65 Cybele
I. Introduction: 24 Themis





Largest fragment of a family (~ 2.5 By old)
Orbiting near 3.2 AU
Diameter ~ 198 km
Dark (reflects only 7% of light)
Rotation period: 8.4 h
I. Introduction: 65 Cybele





Largest of group between 3.3 & 3.7 AU
Orbiting near 3.4 AU
Diameter ~ 273 km
Dark (reflects only 7% of light)
Rotation period: 4.0 h
I. Introduction: Themis Family
• Themis asteroid
family resulted from
a large collision and
contains two small
members that
behave like comets
Elst-Pizarro
176P/Linear
I. Introduction: Themis Family
 Orbits of the two Themis-family active
asteroids not likely to evolve from comets
 Spectra of both Themis-family MBCs
resemble those of the larger family
members and not those of comets
 These small asteroids are true members of
the Themis family; hence, this family
probably contains water-ice
II. Detection of Water-Ice and Organic Molecules
on 24 Themis & 65 Cybele:
Rotationally Resolved Observations of 24 Themis
Infrared Spectra over 7 hours (84% of rotation period)
Rotationally Resolved Observations:
Ice widespread on 24 Themis
Ice
Infrared Spectra over 7 hours (84% of rotation period)
Something is missing !!!
Something is missing !!!
School of
Astronomical
Potions
ORGANICS: the missing ingredient
A 5% of “Ice Tholin” added to the mixture of
water ice and anhydrous silicate works best!
ORGANICS: the missing ingredient
A 5% of “Ice Tholin” added to the mixture of
water ice and anhydrous silicate works best!
Spectra of 24 Themis and 65 Cybele Very Similar
Spectra of 24 Themis and 65 Cybele Very Similar
Ice
Spectra of 24 Themis and 65 Cybele Very Similar
Organics
Exact Composition of Organics is Uncertain:
3.4-micron absorption is produced by C-H bond
3.2
3.3
3.4
3.2
3.3
3.4
3.5
3.5
wavelength (m)
3.6
3.6
IV. Implications on Origin of Earth’s Water
and life
No Water in Early Earth and Mars
• The solids that formed in the accretion zones
of Earth and Mars had a very low water
content
• It has been suggested that most of Earth’s
water came from asteroids and comets
• More specifically, Morbidelli et al. (2000)
suggested Earth’s water came from a single
impact with an object formed in the outer
asteroid belt
Water in Meteorites
Wet
Dry
IV. (cont.)
Implications on Origin of Earth’s Water and life
• If Earth formed dry where did its water come from?
• The composition of Earth’s water is consistent with
asteroidal and cometary contributions
• Main evidence from Deuterium to Hydrogen
isotopic ratios (D/H)
D/H Ratios
10-3
Comets
•HA •HB •HY
Earth Oceans
10-4
C Chondrites (H2O-rich meteorites)
Solar Nebula
10-5
IV. (cont.)
Implications on Origin of Earth’s Water and life
•
Water-rich meteorites have the appropriate D/H
ratio to be a source of Earth’s Water
• The few comets properly observed have D/H
ratios higher than Earth, so comets may have
contributed to raise the D/H from the Solar
Nebula value
• Asteroids and comets likely brought Earth much
of its water….. and more
IV. Implications on Origin of Earth’s Water and life
Surface of Early Earth was Molten Rock
• Magma Oceans
probably
destroyed any
primordial
organics on
Earth
• Meteorites and Comets have significant amounts
of organic molecules:
– the most primitive meteorites are rich in amino
acids, and
– about half of the cometary dust is organic
IV. Implications on Origin of Earth’s Water and life
• Hence, impacts with asteroids and comets, may
have also contributed significantly to the organic
molecule inventory of early Earth
• The discovery of water ice and organics
on 24 Themis and 65 Cybele supports
an asteroidal origin of at least some of
Earth’s water and organic molecules
Any Relevance to Near Earth Asteroids?
Yes, for example:
• 24 Themis is a B-type asteroid, so is near-Earth
asteroid 1999RQ36 the target of NASA’s
proposed asteroid sample return mission:
OSIRIS-Rex
• Our results improve the chances that NASA will
choose this mission for full development ($710
million) in June 2011
• UCF is a member of the OSIRIS-Rex team
V. Conclusions
 Water-ice and organic molecules detected on two
asteroids so far: 24 Themis and 65 Cybele
 Water more abundant on asteroids than expected
 Supports proposed asteroidal origin of Earth’s
water and organic molecules
 Helps understand origin and evolution of life on
Earth and possibility of Earth-like planets around
other stars
 Helps case for NASA’s OSIRIS-Rex mission