Mission: CometRenee French, Amy Jia, Lisa MithunMay 10, 2011

What is a comet?

• Icy body with nucleus, coma, and tail

• Nucleus: ice, dust, small rocky particles, frozen gases

• Size: range from a few hundred meters to tens of km across, irregular

• Origins: Kuiper Belt, Oort Cloud – formation in the outer solar system

• Orbital periods: range from a few years to thousands of years or follow hyperbolic trajectories 1 http://stardust.jpl.nasa.gov/science/why.html

2 Image: http://t3.gstatic.com/images?q=tbn:ANd9GcT2P3_P9nskrj4QjUJLDaK93Hd5FMzDL27ly9OYozgBk6M_nsTc8A

 Relationship to life on Earth

Why do we think life could have originated in this way?

•Collisions▫ Common in early solar system▫ Craters on the moon▫ Shoemaker-Levy & Jupiter

    • Comets could contain:▫ Untouched samples of early solar system, proto-planet/nebular material▫ Water ▫ Organic compounds ▫Amino acids

Miller-Urey Experiment   

1 http://stardust.jpl.nasa.gov/science/why.html

2 Image: http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/Schwassman-Wachmann3-B-HST.gif/220px-Schwassman-Wachmann3-B-HST.gif

Evidence that it could seed life

• Not necessarily panspermia

• Also, while unlikely, not ruling out life 1 m down

▫ Though conditions are extreme, there would be shielding of solar radiation

• Discovery of glycine in comets is the basis of a theory and not definitive

• A long way from glycine to life

• Strengthens Rare Earth Hypothesis

1 http://stardust.jpl.nasa.gov/science/life.html2 Image 1: http://t0.gstatic.com/images?q=tbn:ANd9GcTv2viQtU-IJyf3IUaQJyqIf1lmpg_1sshNDF9KoYClB4L0x5T1rg 3 Image 2: http://www.daviddarling.info/images/glycine.jpg

Stardust at comet Wild 2 (2006)

- Samples collected with aerogel    - highly porous    - density of air: slows particles and prevents melting or vaporization. - Instruments    - navigational cameras    - dust analyzer        - mass spectrometer        - real time info    - dust flux/size distribution      monitor    - dynamic science experiment        - determine mass of comet               density ->0.6g/cm^3

Burnett, Nasa Returns Rocks from a Comet, 2006

http://www.nasa.gov/mission_pages/stardust/spacecraft/index.html

Track variability

 - Track morphology reflects physical properties of particle, size dependent•cohesive material made "carrot-type" tracks•poorly consolidated material made "turnip-type" tracks•fine grain material or volatiles made bulbous cavities

Brownlee et al., Comet 81P/Wild 2 Under a Microscope, 2006

Horz et al., Impact Features on Stardust: Implications for Comet 81P/Wild 2 Dust, 2006

Stardust findings-Composition    - anhydrous olivine (Fo4-Fo100),

pyroxene, troilite(FeS) most abundant

    - labile organics rich in O, N• naphthalene, phenanthrene, pyrene -> resembles Murchison

    - amines methylamine and ethylamine

- Ejected particles indicate no previous heating, compaction or aqueous alteration

-Cohesive and self supporting surface - not rubble pile

 

Brownlee et al., Comet 81P/Wild 2 Under a Microscope, 2006

Sandford et al., Organics Captured from Comet 81P/Wild 2 by the Stardust Spacecraft, 2006

Stardust rendezvous with Tempel 1 

- Flew past Tempel 1 on Feb 15, 2011

- Analyzed surface changes from impact and Sun approach

http://www.nasa.gov/mission_pages/stardust/main/index.html

Deep Impact and Tempel 1 (2005)- 370 kg object created a crater 150 m diameter, 30 m deep

-Composition• amorphous/crystalline silicates, amorphous carbon, carbonates, phyllosilicates, polycyclic aromatic hydrocarbons, water gas/ice, sulfides• consistent with solar and chondritic abundances• indicates mixing over large distances in protosolar disk

- A total of 5e6 kg of water and 10-25e6 kg of dust were lost from impact

http://www.nasa.gov/mission_pages/deepimpact/main/

Can organic materials survive impact?

• Water and organic molecules may survive impact

o If low enough angle

o Sufficient drag from Earth’s atmosphere to slow comet

• Early bombardment was heavy enough to deliver a significant amount of intact organic material and water

Blank et al, 2001

Blank et al: Collision Study• Jennifer G. Blank • Department of Earth and Planetary Science • University of California, Berkeley

• 3 year project to design a steel capsule that would not rupture when hit with a bullet traveling 1.6 km/sec.

• The target was a 2 cm wide stainless steel 0.5 cm thick filled with 5 amino acids and a drop of water

• able to withstand about 200,000 times atmospheric pressure without bursting

Schematic diagram of Blank et al.'s apparatus. The red arrow indicates the projectile fired from the breach toward the stationary target (inset). The 3 smaller red triangles indicate transducer pins that measure the velocity of the projectile as it passes. Upon impact, the sample container flies backwards into the recovery area, where it is trapped as gently as possible in layers of felt.

NASA, 2001

Blank et al: Results• Most amino acids survived

the simulated comet collision

• Created every possible combination of dipeptide, many tripeptides and some tetrapeptides

• Saw variations in the ratios of peptides produced depending on the conditions of temperature, pressure and duration of the impact.

Nir Goldman et al: Study of Comet Shockwaves• Studied molecular dynamics simulations of shock waves

after a comet strike to see if organic materials could survive the conditions during and after impact

• The team found that the shock waves from a comet's impact can promote short-lived C-N bonded oligomers

• When the pressure dropped after impact, these oligomers break up to form stable complexes containing the amino acid glycine. 

• Evidence for complex organic chemistry under conditions of extreme pressure and temperature

Royal Society of Chemistry, 2010

Past Missions• Stardust mission, 1994:

collected interstellar dust and particles on the surface of the comet using aerogel collectors

o Evidence of life more likely to be found inside comet

Photo (top): www.optics.rochester.eduPhoto (below): astrophys-assist.com

Past Missions Deep Impact • Launched in 2004• NASA• In 2005, released an impactor

that collided with 9P/Tempel’s nucleus

• Excavated debris from interior• 2006, sample capsule returned to

Earth• Photographs of impact showed

composition of comet to be dustier and less icy

• unable to image the crater because of the unexpectedly dense and opaque debris cloud

• Reused spacecraft NASA, 2006

Current MissionsRosetta• European Space Agency • 2004-2014• Comet 67P/Churyumov-

Gerasimenko• will land a probe on the comet

and drill for core samples• First probe to orbit a comet • First deep space mission to rely

on solar panels for power, rather than nuclear-generated power

• 2 Fly-by missions of asteroids completed

Spacetoday.org

Current Missions

Champollion / Deep Space 4 (Cancelled in 1999)• April 2003• NASA• planned to go into orbit

around nucleus of Tempel 1 in April 2006.

• 100 kg lander would land on surface and drill 1 meter down to collect samples of the nucleus

• On-board analysis with results transmitted to Earth

(NASA, 2010)

Next Mission• Our plan: To land a probe on the comet and drill one

meter down to sample the interior of the comet

• Technical Issues:

o gentle landing to avoid harming probeo Reduced speed to photograph cometo contamination of sampleso Choosing suitable comet

Future mission: which comet?- Tempel 1    - water (clays, carbonates)    - organic molecules     - hypothesized to have formed in Uranus/Neptune-Oort Cloud      region (interior chemistry)    - Short period (5.52 years)

- Good agreement between Tempel 1 and Hale-Bopp compositions -> non-uniqueness

Image from Ahearn et al., Whence Comets?, 2006

Costs• Rosetta (2004):

o Projected: $900 million USo Actual: $1.2 billion US (over $80 million in delays)

• Deep Impact (2004):o $328 million total

• Stardust (1999):o $199.6 million totalo $150 million: cost of development and construction

of the spacecraft.o $30 million to reuse spacecraft

Projected Costs

• $1.5 billion total

Pros:• Lower cost than most deep space missions• reuse spacecraft• “gravity assist” trajectory decreases fuel costs• Technology for sampling and analysis already exists

Cons:• "gravity assist" trajectory extends timeline• Delays significantly increase cost

The next 15 years

• Assess what the major problems were last time and what we should do differently • Generate ideas on multiple targets to reduce cost or plans to recycle probe•Build new probe• After determining target comet and trajectory, determine mission length▫ A 6-10 year mission would allow for 5-9 years of building and planning• Prepare technical equipment▫ Engineer a tool small enough to add to the probe ▫ Ability to drill, scoop, keep safe from re-entry and keep clean

Based on what we found, did a comet seed life on Earth?