Current Research Projects
Summary of Previous Research
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.
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.
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).
In 2010, I worked 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 also observed low numbered (<1000) asteroids with poorly constrained rotational periods in collaboration with Jackson State University observatory.
Since 2014, I have been working with Bruce Gary and Tom Kaye, private observers from Sierra Vista, Arizona, on lightcurve observations of small NEAs (<150 meters). Each lunation our group observes about 3-4 NEAs using 14" telescopes. We also have access to a 32" telescope at Junk Bond Observatory to observe fainter targets. Typical limiting magnitude for the 14" telescopes is 17.2 V mag and two magnitudes fainter for the 32"
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:
Currently I am PI of a NASA NEO Observation Program grant to characterize small NEAs using lightcurve and spectroscopy. We are primarily using the NASA IRTF and able to observe down to V Mag 20 for Near-IR spectroscopy 0.7-2.5 microns). Our goal is to study the compositional diversity of targets in this size range.
Recently, the Chelyabinsk impact provided important clues into the origin of the Baptistina Asteroid Family. Chelyabinsk meteorite contains significant shock and impact melt components apart from unshocked LL chondrite material. I was able to show that shock darkening can explain the spectral properties of Baptistina Asteroid Family and published a paper in Icarus regarding this in 2014.