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

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

Outline

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

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: 24 Themis

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: 65 Cybele

• Themis asteroid family resulted from a large collision and contains two small members that behave like comets

I. Introduction: Themis Family

Elst-Pizarro

176P/Linear

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

I. Introduction: Themis Family

Infrared Spectra over 7 hours (84% of rotation period)

II. Detection of Water-Ice and Organic Molecules on 24 Themis & 65 Cybele:Rotationally Resolved Observations of 24 Themis

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!

A 5% of “Ice Tholin” added to the mixture of water ice and anhydrous silicate works best!

ORGANICS: the missing ingredient

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

3.2 3.3 3.4 3.5 3.6

3.2 3.3 3.4 3.5 3.6 wavelength (m)

Exact Composition of Organics is Uncertain:3.4-micron absorption is produced by C-H bond

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

• 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)

IV. (cont.)Implications on Origin of Earth’s Water and life

D/H Ratios10-3

10-4

Earth Oceans

10-5

Solar Nebula

•HB •HY •HA

C Chondrites (H2O-rich meteorites)

Comets

• 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. (cont.)Implications on Origin of Earth’s Water and life

Surface of Early Earth was Molten Rock

IV. Implications on Origin of Earth’s Water and life

• 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

• 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

IV. Implications on Origin of Earth’s Water and life

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

Any Relevance to Near Earth Asteroids?

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