Dr. Joshua Emery

Planetary scientist Josh Emery sweats the small stuff. The larger bodies of our solar system – planets and moons – have been tortured and twisted in childhood by their internal heat, and therefore offer only a distorted view of the conditions under which they formed. Small bodies like asteroids, on the other hand, haven’t undergone such metamorphosis. Consequently, they provide good evidence about what happened in our neighborhood more than 4 billion years ago.

Josh uses the SpitzerSpaceTelescope to study asteroids in the outer solar system (beyond Mars) by examining their infrared spectra. Many of these get brighter as one looks deeper and deeper into the red end of the spectrum, and this is thought to be due to complex organic molecules that coat their surfaces. Josh is using a variety of ground-based telescopes, as well as Spitzer, to verify this hypothesis. If asteroids are wrapped in materials that are essential to the start of life, then perhaps life’s ingredients are common in many planetary systems.

Adopt a Scientist Opportunity

Here’s your opportunity to be a part of an astronomical observing project, including a trip to the world's premiere observatory site – Mauna Kea, Hawaii. You’ll want the full package, which includes a detailed tutorial on asteroids and organics in the solar system, making a hands-on contribution to developing the observing program and writing the
observing proposal, traveling to the telescope, and conducting the observations with Josh. You’ll also assist with the processing and analysis of the data afterward. 

Or skip the academics and just travel to Mauna Kea with Josh for the observations. Note that the full package will also give you co-authorship of a scientific paper!

The Mauna Kea observatories are at 14,000 ft elevation, so there are some physical limitations – no one with known heart problems or trouble with high elevation is allowed. Typical observing runs last 3 nights, but could be as long as 6. Accomodations are located at 9,000 ft on the flank of the dormant volcano, and are dormitory style. Cafeteria style food is provided as is phone and internet connectivity.

Projects

"Investigation of Suitable Targets for Space Missions to Near-Earth Objects"

JPL 1276028

The Near-Earth Objects (NEOs) are small bodies of the Solar System which periodically approach or intersect the Earth's orbit. The NEO population is supposed to be continuously replenished by asteroids and comets and is believed to be one of the principal sources of meteorites found on the Earth. As a consequence, the study of the physical properties of NEOs is interesting for scientic goals, to investigate the nature of the whole population of small bodies of the Solar System. It also provides essential information for technological purposes, considering the potential hazard that these objects constitute to our planet and the development of suitable mitigation strategies both on Earth and from space.  In the last years, scientic and technological goals have pushed space agencies to plan and launch space missions to NEOs. In this respect, observations investigating the physical and thermal structure of NEOs are needed in support of future space missions. Due to the wide variety of the orbital characteristics of NEOs, target selection must be able to guarantee both technical feasibility and high scientic return. We therefore propose to carry out spectroscopic observations, in the mid- and far-infrared wavelength range, of NEOs characterized by a high degree of accessibility for a space mission. We have selected 13 targets accessible from Earth for space missions that amount to a total of 24.5 hours of IRS observations to obtain spectroscopic data between 5.2 and 38 microns. The aim of these observations is the investigation of the surface composition and thermal structure and the determination of the albedo and diameter of each selected target.

"IRS Spectroscopy of M-Class Asteroids"

JPL 1276503

We will conduct IRS 5.2--38 micron observations of the emission spectra of 27 M asteroids. Although the visible and near-IR spectra of these asteroids are nearly featureless, ten of these asteroids are now known to have hydration features at 3 micron (Rivkin et al., 2000) that are absent in the spectra of 15 others. We believe that high S/N spectroscopy of these asteroids in the mid-infrared is likely to reveal key compositional information not available in the near-infrared. In particular, it has the potential to resolve the question of whether the M-asteroid population is composed primarily of silicates, or metals, or both. This compositional information in turn is likely to lead to a better understanding of how widespread igneous differentiation was among the parent bodies of the current asteroid population.

"Surface Compositions of KBOs, Centaurs, and Low Albedo Asteroids: Constraints from IRAC Reflectance Measurements"

JPL 1276917

We indend to measure broadband fluxes of a sample of Kuiper Belt Objects (KBOs), Centaurs, and low albedo asteroids with IRAC. Ground-based spectra have been recorded from the visible to 2.5 microns for all objects in the target list, but spectral models admit a range of possible compositions. Reflectance in two or, in some cases, three bands (3.6, 4.5, and 5.8 microns) will allow discrimination between possible spectral models, thereby constraining surface compositions. For several objects, thermal emission will be detected in the 8.0-micron band. The simultaneous measurement with IRAC of both reflected and emitted flux will permit estimation of size and albedo for these objects. Compositions of these primitive bodies allow analysis of conditions in the outer solar nebula during formation, diversity in the Kuiper Belt, and possible dynamical and evolutionary links between KBOs, Centaurs, and low albedo asteroids.

“Greeks Bearing Gifts: Determination of the Surface Compositions of Trojan Asteroids from NIR Spectroscopy and Spectral Modeling”

NNG05GG80G

The goal of this task is to investigate the surface compositions of Trojan asteroids, to be accomplished by spectral mixing modeling of a rich set of as-yet unpublished near-infrared (NIR) reflective data as well as through collecting and modeling new spectral data over the wavelength range 0.8–4.0 µm using ground-based observatories. The new observations will focus mainly on smaller Trojans than have previously bee studied. Smaller objects are statistically more likely to have undergone recent collisions, and therefore are expected to have “fresh’ surfaces that reveal bulk (primordial) composition. We expect to observe 50 new Trojans, tripling the current dataset. Modeling these and the unpublished data will increase the number of Trojan asteroids that are quantitatively modeled by a factor of 5 or more.

"Outer Solar System Bodies"

NNA05CS63A

This project consists of two main tasks:

One is to collect as much information on the composition of the Solar System bodies for which data is already available or will become available in the near future from both ground and space-based telescopes, as follows, is being conducted by Cristina Dalle Ore:

• Bring Pluto into the picture and compare results with Triton: are they really so similar or is there an underlying difference (Charon?) that makes those two worlds two independent problems?
• Continue the study of more asteroids as more data become available: our quantitative modeling studies of asteroid spectra allow us to explore the amounts of various minerals present on the surfaces of these bodies, and to search for the presence of organic constituents that may have some connection to the prebiotic history of the Earth.
• Investigate more Centaur and Kuiper Disk objects as data become available to learn more about the history of the materials that were condensed at the edge of the Solar System and that can give us hints on the early Solar System evolution.
• Pursue previous modeling efforts to determine the surface composition of more of the saturnian satellites. Compare results among neighboring satellites to infer possible interactions.

The other task, conducted by Joshua Emery, is as follows:

This task will investigate the physical structure and composition of several classes of solar system objects. Measurements of thermal fluxes at several wavelengths will provide the means of deriving sizes, albedos, and/or thermal properties of the surfaces of a large number of Kuiper Belt Objects (KBOs), Centaurs, icy satellites of the outer planets, and Pluto. Surface compositions of a moderate number (~30) of asteroids of several dynamical classes (near-Earth, main belt, Trojan, extinct comet candidates), a few of the brightest Centaurs and KBOs, icy satellites of the outer planets, and Pluto will be studied with thermal emission spectroscopy. Reflected fluxes at 3.6, 4.5, 5.8 and 8.0 m m will be obtained for the icy satellites and Pluto as additional constraints on surface composition. The satellites of Saturn will also be studied using near infrared reflectance spectroscopy. This ambitious program is already in progress, and will be carried out using two spacecraft: The Spitzer Space Telescope and the Cassini spacecraft. Spitzer was launched in August 2003 into an Earth-trailing, heliocentric orbit. It is currently functioning well and returning data. The science payload consists of three instruments. The infrared camera (IRAC) collects images in 4 bands centered at 3.6, 4.5, 5.8, and 8.0 m m. For the surface temperatures of most objects in the outer solar system, fluxes measured at these bands will be dominated by reflected sunlight. The infrared spectrograph (IRS) can measure low resolution (R~60–100) spectra over the range 5.3–40µm, and high resolution (R~600) spectra over the range 10–37 m m. Asteroid fluxes in this range are dominated by thermal emission. Small, colder objects in the outer solar system have sufficient emitted flux only at the longer end of this range to be measured by Spitzer. The Multiband Imaging Photometer for Spitzer (MIPS) provides imaging photometry at 24, 70, and 160µm, and very low resolution (R~15–25) spectroscopy over the range 55–96µm. Fluxes of solar system objects are dominated by thermal emission at these long wavelengths. The Cassini spacecraft was launched in 1997, and is due to arrive at Saturn and enter orbit in June 2004. During its mission, Cassini will record images and spectra of the icy satellites of Saturn. The Visual and Infrared Mapping Spectrometer (VIMS) instrument measures spectra over the range 0.3–5.0µm. Radiation from the moons of Saturn is dominated by reflected sunlight over this range.

This work addresses several outstanding problems in planetary science related to each of the specific groups of objects mentioned above, which will, taken together, also provide deeper insights into the origin and evolution of our solar system.