SSERVI scientists are working on problems associated with all the places humans might go in the near future: the Moon, Near-Earth Asteroids, Phobos and Deimos, and ultimately Mars. The exploration of these worlds helps science, and science, in turn, assists exploration.


Below is a flavor of the work each of the nine domestic SSERVI teams has been doing in the past year.

Bill Bottke, Principal Investigator of SSERVI’s ISET team at SwRI

Hal Levinson at SwRI has been leading research on a particular aspect of planet formation called “pebble accretion.” Suppose you have a millimeter-sized object flying in space and it goes by something the size of Mars, which gives it a small gravitational kick but otherwise not much happens to it. Traditionally, this is the kind of dynamics that planet formation models deal with.

“Pebble” Moving without Gas Drag

*Orbit perturbed by protoplanet, but no accretion

But in a solar nebula, these particles feel a headwind, which slows them down slightly, causing them to spiral down to their doom. Effectively what this means is that the accretion radius for bodies that get to a certain size can be very large. In the modeling, something very small can become very huge in very short time scales. The team implemented this new “pebble accretion” theory into a new modeling code called LIPAD.

Gas Drag and Pebble Accretion

*Pebbles feel headwind, become captured by large bodies

Here simulations of the inner and outer solar system are shown together. Small pebble-sized objects grow up to become larger objects, then proto-planetary objects, and ultimately start to grow into planets.

Making Planets Using Pebbles

*Planets grow from tiny “pebbles” affected by gas drag.
*Few smaller planetesimals, so early bombardment may be limited to large rare impactors.
-from Bottke et al. (2010); Levison et al. (2015); Levison, Kretke, Walsh, and Bottke (2015)

In the end, we have a system of planets that looks like what we have today. This new model represents an exciting way forward, with new ideas that challenge our preconceived notions about how planet formation works.

Pebble Accretion, Planets, Asteroid Belt
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*Model naturally produces low mass Mars and asteroid belt.
*Most of the action is done in < 100 Myr (~4.45 Ga)
-from Bottke et al. (2010); Levison et al. (2015); Levison, Kretke, Walsh, and Bottke (2015)

David Kring, Principal Investigator of SSERVI’s CLSE team at LPI

Researchers at the Center for Lunar Science and Exploration have been testing some of the theories discussed above.

In models of Earth’s formation we have two giant proto-planets crashing together, which creates a debris disk, and the Moon forms from the accretion of this material.

Source of Water in the Lunar Interior

The Moon gets hit from other asteroids and comets in the early stages of planetary differentiation, which likely delivered water to the interior of the Moon.

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The team has found that most of the water inside the Moon was delivered by wet asteroids during the early evolution of the Moon, ~4.5-4.3 billion years ago, while comets contributed only a small proportion of volatiles to the interior of the Moon.

Andy Rivkin, Principal Investigator of SSERVI’s VORTICES team at APL

Lunar True Polar Wander Inferred from Polar Hydrogen

Several NASA spacecraft have detected hydrogen signatures at the lunar poles. One of the things that have been found is a hydrogen signature that is symmetrically off-set from the lunar poles.

The lunar poles have permanently shadowed regions, and hydrogen molecules hopping around on the Moon may eventually fall into a cold trap at the bottom of a permanently shadowed crater. When lunar ice is exposed to direct sunlight it evaporates into space, making it a very sensitive marker of the moon’s past orientation. When researchers detected hydrogen signatures in sunlit areas that matched symmetrically at both poles, they inferred that the Moon’s axis had shifted roughly 6 degrees over time.

An off-axis abundance of hydrogen at the moon’s north pole (left) is matched symmetrically at the south pole (right).

The path of lunar polar wander is seen in the present-day H distribution

Over eons, the tilting Moon allowed sunlight to slowly creep into once shadowed areas, effectively “painting” a path of stable ice along which the axis moved.

This is the first physical evidence that the Moon underwent such a dramatic change in orientation and implies that much, or all, of ice on the Moon is billions of years old.

Carle Pieters, Principal Investigator of SSERVI’s SEEED team at Brown University

Scientists have found evidence of basaltic volcanism on the Moon and have been modeling how these volcanic features formed.

Distribution of Volcanic Deposits on Moon

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*Mare emplacement and secondary crust formation. Substantial volcanism 3-4 Ga. Much less for 1-3 Ga.

Thanks to GRAIL spacecraft data, we now have good estimates for the thickness of the Moon.

Generation, Ascent & Eruption of Basaltic Magma on the Moon
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*New GRAIL crustal thickness data and LRO/LOLA/LROC data permit a revised synthesis of the generation ascent and eruption of basaltic magma on the Moon
*Nearside-farside distribution of mare basalt deposits is very likely related to differences in crustal thickness.

Early on in the Moon’s formation there was a basaltic source that melted and created gas to push its way up to the surface. If the crust was too thick, the molten material never made it to the surface, but if the lunar crust was thin, it erupted into a basaltic volcano!

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*Host of volcanic features (small shields, cones, domes, pit crater chains, pyroclastic deposits, floor fractured craters, etc.) linked to behavior of dikes in the shallow crust of the Moon as they intrude, stall, degas and erupt.

Bill Farrell, Principal Investigator of SSERVI’s DREAM2 team at GSFC

Orion Outgassing and Asteroid Interaction (ARM)

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Artist rendering of Orion capsule obiting around astronaut performing asteroid surface science

It turns out that both the spacecraft and the astronaut’s spacesuit slowly leak oxygen, and larger amounts of oxygen can escape every time an astronaut goes in or out of the spacecraft’s hatch. This raises an interesting issue of water contamination. If NASA plans to have astronauts interacting with asteroids, how much of that oxygen will stick? And can we avoid contamination so that we are not changing the samples they collect? The DREAM2 team is working hard to answer these and other questions related to asteroid-astronaut interactions.

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The amount of water that ‘sticks’ is a function of the activation energy of the surface water adsorption and temperature.
Initial water flux incident at surface assumed to be shuttle-like at 1 km distance (5 x 10^14/ m2-s) [from Farrell et al., 2016, in review]

Tim Glotch, Principal Investigator of SSERVI’s RIS4E team at Stony Brook University

Quantitative Geomorphology and Planetary Surface Exploration

Credit: S. Scheidt

*An analog for the formation of sinuous channels, platy lava flow surfaces, and streamlined islands
*Highlights value of stereophotogrammetry for quantitative geomorphology and planetary surface exploration
*Virtual geologic outcrops can be directly compared to hi-res topographic models made from MRO stereo data

Remote sensing of a lava flow in Hawaii resulted in high res topography data and optical properties of the area. These preliminary studies illuminate the nature of the lava flow and identify the most interesting regions for follow-on study, so scientists can explore those regions more efficiently.

*LiDAR scan of a Hawaiian lava tube used to create this 3D Digital Terrain Model (DTM) by Brent Garry.
*A terrestrial analog for plains-style volcanism in southeastern Mare Serenitatis on the Moon
*Precursor pit missions critical to identify possible link to subsurface void space
*Inflation of viscous sheets considered as potential in-situ lunar habitats

Jennifer Heldmann, Principal Investigator of SSERVI’s FINESSE team at NASA Ames Research Center

Field Investigations to Enable Solar System Science and Exploration

How can we help astronauts do the best fieldwork possible when they go to remote sites? Craters on the Moon is a unique analogue environment in Idaho where Apollo astronauts went to train. When Apollo astronauts went to the moon they had a mission control, but they also had a team of scientists in a back room that would provide input to the astronauts. Scientists would talk amongst each other but couldn’t fill the Astronaut’s ears with scientific discussion, so there had to be procedures for how they provide information to the astronauts, how information goes back and forth, what’s the best way to get the most interesting samples, but then also let the astronauts do their jobs. So the FINESSE team has conducted field studies that include extra-vehicular activities, a mission control room, and a science operations center, in order to simulate field deployments and test new technologies and procedures.

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In-simulation field deployment (June 2016)

Mihaly Horanyi, Principal Investigator of SSERVI’s IMPACT team at University of Colorado, Boulder

Electrostatic Dust Transport Reshapes Surfaces of Airless Planetary Bodies

The IMPACT team has conducted laboratory experiments to bring closure to a long-standing issue of electrostatic dust transport, explaining a variety of unusual phenomena on the surfaces of airless planetary bodies, including observations from the Apollo era to the recent Rosetta comet mission. The research explains how dust may be transporting across vast regions above the lunar surface and rings of Saturn, without winds or flowing water. Emission and re-absorption of photo/secondary electrons at the walls of micro-cavities formed between neighboring dust particles can generate unexpectedly large charges and intense particle-particle repulsive forces, which can mobilize and lift dust particles off the ground.

Top: Lunar horizon glow seen in Surveyor 7 image may have been caused by sunlight scattering in a cloud of electrostatically lofted dust particles. Middle: Laboratory observations of electrostatically-lofted dust particles; surfaces smoothed as a consequence of dust mobilization. Bottom: Micron-sized dust particles jump up to several centimeters high when exposed to plasmas in laboratory. Credit: Wang et al/ U.C. Boulder/LASP

Dan Britt, Principal Investigator of SSERVI’s CLASS team at University of Central Florida

Asteroid Regolith Simulants

CLASS has been preparing asteroid simulants to study regolith properties and how they behave in micro-gravity studies.

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*CLASS has partnered with Deep Space Industries (DSI) to develop a family of asteroid regolith simulants for engineering and ISRU development.
*We developed a prototype simulant based closely on the mineralogy of CI carbonaceous chondrites.
-Our approach is to use the type meteorites as a guide to mineralogy and texture.
-Under Phase II SBIR funding we are developing a total of 6 simulants: CI, CM, CR, CV, C2, L-chondrite
-Production will depend on demand
*Prototype results
-Mineralogy, texture, albedo, volatile release patterns are good analogs for the type meteorite.
-Strength, density, porosity are also good analogs.
-The stuff is also REALLY dirty…..just like carbonaceous chondrites.

The team has been involved in the Strata-1 experiment on the International Space Station (ISS), which features multiple transparent tubes that are partially filled with regolith simulants which are exposed to extended microgravity and the ambient vibration environment on ISS. This will help improve our understanding of regolith that astronauts and/or hardware will encounter on upcoming NASA missions.

Strata-1: The ISS is one big “asteroid”
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*Uses the ISS gravity and vibration environment to simulate asteroid conditions – experiment is passive!
*4 tubes mounted in a rack on the ISS
*glass beads & shards to compare to simulations
*realistic particle size, composition
*Video data used to analyze layering, particle motion

Asteroid simulant shows motion due to vibration environment

For more, watch a recording of the presentation at the Exploration Science Forum: SSERVI Year in Review by Bill Bottke, PI of the ISET team.

Posted by: Soderman/SSERVI Staff
Source: SSERVI/ESF 2016

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