• Mineralogical Investigation of Asteroid (4) Vesta using Dawn Framing Camera
  
• Photometric and Spectral Phase Functions of Dwarf Planet (1) Ceres
  
• Compositional Characterization of Baptistina Asteroid Family

 Astrometry

My earliest work in planetary sciences began as an undergraduate student in India when I studied the nature of lunar rays around the crater Proclus. This observational study gave me valuable experience in working with telescopes and imagers. Based on this experience, I started exploring the possibility of conducting astrometric observations of near-Earth asteroids and comets using small telescopes. Comet Shoemaker-Levy-9 had impacted Jupiter a few years earlier and the U.S. Congress mandated NASA to discover 90% of all near-Earth objects (NEOs) within 10 years. This presented an urgent need to discover and catalog new NEOs.

Given the limited opportunities I had to do planetary science in India, I had few avenues for funding this research. I started a private foundation and raised $6,000 to build an observatory for studying NEAs from India. The foundation, Spaceguard India, is a non-profit organization dedicated to educating the public on the threats of NEAs. With the help of Dr. Tom Gehrels and Mr. Roy Tucker at University of Arizona, I was able to discover 23 Main Belt asteroids and submit several thousand accurate astrometric positions of asteroids and comets to the minor planet center. One of these asteroids was later named Bharat (India) in honor of my country.

I continued doing astrometric observations after joining the graduate program at the University of North Dakota’s Space Studies department. Some notable projects I have contributed to include the ground-based observations of Deep Impact Spacecraft in collaboration with Dr. Steve Chesley, JPL, which made it possible to navigate the impactor on a collision course with the comet. Astrometric observations made by me of potentially-hazardous asteroid (99942) Apophis were helpful in refining its orbit and eliminating the possibility of an Earth impact in 2029.

Photometry

By early 2003, it became clear that NASA would probably fulfill the Spaceguard goal set by Congress and there was a pressing need to do physical characterization of NEAs being discovered. As the next step, I started working on rotational lightcurves of NEAs using photometric observations during the first year of my graduate program at UND. This work was done in collaboration with Dr. Petr Pravec, Academy of Sciences of the Czech Republic, and Dr. Alan Harris, Space Science Institute, who are the leading experts on asteroid rotational studies. I was one of 60 international collaborators on the project who regularly conducted photometric observations of a pre-selected sample of asteroids to determine their rotational periods based on their lightcurves. A majority of this original work was done from the Badlands Observatory in South Dakota in collaboration with my colleague Mr Ron Dyvig.  

My volunteer efforts paid off when I discovered the project’s first binary NEA, 2005 AB (Reddy et al, 2006). 2005 AB turned out to be an interesting object when spectroscopic and dynamical studies by De Meo and Binzel (2008) suggested that the object could be a dead comet nucleus. Radar observations from Arecibo radio telescope of 2005 AB suggested a diameter of 1.9 km. Following this, I discovered my second binary NEA (7088) Ishtar using the same technique. Using observations, Pravec et al. (2006) were able to suggest that 15±5% of all NEAs were binary objects. This has important implications for their formation mechanism and impact hazard assessment.

Apart from these, I also discovered/co-discovered main belt binary asteroids (4951) Iwamoto, (1338) Duponta, (32008) 2000 HM53, (2486) Metsahovi, (3073) Kursk, (9617) Grahamchapman, and (1717) Arlon using photometric techniques. All these discoveries and observations contributed toward better understanding of the nature of binary asteroids. These include that the most efficient way to form small binary asteroids (NEA and Main Belt) is by YORP spin-up (assymetrical re-radiation of solar flux), and that small Main Belt and near-Earth asteroid binaries share the same rotational characteristics. These results were summarized in Pravec et al. (2008).

I am currently working with Ken and Reid Archer at the Ironwood Observatory (F60) and Ironwood Remote Observatory (F59) in Hawaii on photometric phase functions for Asteroid (4) Vesta using DAWN Filters. We are also observing low numbered (<1000) asteroids with poorly constrained rotational periods in collaboration with Jackson State University observatory. First results of this work can be found on my blog.

Spectroscopy

Near-IR spectroscopy of asteroids has been the main focus of my graduate studies for the last five years. Characterization of asteroid surface material is based on interpretation of diagnostic absorption features that are related to specific mineral species. Low resolution (R=100) visible and Near-IR spectroscopy (0.30-2.5 µm) is the most sensitive tool to accomplish this task. I joined the spectroscopy group led by Dr. Mike Gaffey at the Department of Space Studies, University of North Dakota, in fall of 2003 for my Masters degree. My thesis work focused on mineralogical studies of olivine-rich asteroids.

The discovery of olivine-rich asteroids is of considerable interest because pure olivine generally forms only due to magmatic differentiation and is the major constituent of the mantles of most differentiated bodies. Another interesting aspect is that in order for the mantle to be exposed, the parent body must be fragmented or its deep interior exposed by large impacts. I worked on two olivine-rich asteroids (246) Asporina and (446) Aeternitas and determined their composition to be more Iron-rich than terrestrial olivines. This suggests that these asteroids experienced at least partial melting temperatures (T ≥ ~950ºC) in the region of the main belt. Using this information, one can start constructing a crude thermal gradient map of the asteroid belt. This rests on the assumption that most large asteroids in the main belt have remained in their current location over the last 4.5 billion years. Using spectral data from other sources, it appears that the early solar system heating event was very heterogeneous. This is supported by the presence of differentiated asteroids (1459 Magnya) in the outer main belt that were formed at temperatures higher than 1000ºC.

For my Ph.D. dissertation work, I focused on three main areas:

• Physical characterization of Near-Earth Asteroids
• Baptistina Asteroid Family-Relation to K-T Impactor
• Mineralogy of pyroxenes
  

Near-Earth Asteroids: In 2005, I started working on physical characterization (composition, albedo, size, and thermal properties) of near-Earth asteroids using the NASA Infrared Telescope Facility (IRTF). Physical characterization of NEAs is very important for impact hazard assessment because the composition and size of an object has direct implications for the extent of damage on the ground. With the help of my advisors, Drs. Mike Gaffey and Paul Abell, I was able to develop a new technique to constrain the composition, albedo, and size of an NEA from a single near-IR spectrum (0.70-2.50 µm). For NEAs with albedo <20%, the Wien thermal tail of the Planck Curve is shifted to near-IR wavelengths (2.0-2.50 µm) due to higher surface temperatures in near-Earth (1 AU) space. Using thermal models, I was able to estimate the albedo and size of nearly 40% of all NEAs observed with an accuracy of 10% for sizes compared to radar estimated diameters. The observation and data reduction techniques I use have enabled me to obtain lab-quality spectra of NEAs down V Mag = 17.5 using the NASA IRTF.

Baptistina Asteroid Family: In 2007, Bottke et al. announced in Nature that the object that hit the Earth 65 million years ago, leading to the extinction of the dinosaurs, was created when the parent body of asteroid 298 Baptistina was catastrophically disrupted ~160 Myr ago creating the Baptistina Asteroid Family (BAF). This discovery was of great significance because it was the last great extinction in geologic history.  A key line of evidence linking 298 Baptistina and K-T impactor was their supposedly similar composition (CM2 carbonaceous chondrites). Composition of 298 Baptistina was assumed from C or X taxonomic classification based on visible spectra. I examined the visible spectrum of 298 and clearly found evidence for a weak 0.90 µm band suggesting a silicate dominated surface. Further spectral observations (0.7-4.2 µm) with the NASA IRTF clearly showed that 298 Baptistina was not a C-type asteroid as suggested by Bottke et al. (2007) but an S-type with the mineral pyroxene on its surface. I collaborated with Dr. Bottke after my findings and we published a joint paper titled "Composition of 298 Baptistina: Implications for the K/T impactor link" for a special issue of Meteoritics and Planetary Science. I am studying other members of this family, which are also turning out to be S-type.

Pyroxene mineralogy: Apart from the telescopic observations summarized above, I have done extensive work on lab spectral calibration of minerals for interpreting remote sensing data from telescopes. A majority of this work is in collaboration with Dr. Ed Cloutis, University of Winnipeg, Canada. We have measured visible-NIR spectra of over 90 different pyroxenes with the goal of estimating the chemistry of this mineral from asteroid spectra enabling us to constrain not only the formation temperature but also the redox state of the nebula where an object formed. Our goal is to use this technique to address key questions in planetary sciences regarding the nature and origin of the early solar system heating event, which has significant implications for the development of conditions that led to the evolution of life on Earth.

Binary Asteroids: After discovering/co-discovering half dozen binary asteroids, I was curious to see if there is any compositional selection effect to their formation. For example, are weaker C-type asteroids more likely to form binaries due to YORP effect than M-types (assumed to be metallic)? So far, I have observed about a dozen small main-belt and NEA binaries and have not found any affinity for a particular taxonomic type. This finding seems to be telling us something fundamental about the lack of internal strength in small asteroids, regardless of their composition.