About

Dimitar Sasselov is the Phillips Professor of Astronomy at Harvard University and the Director of the Harvard Origins of Life Initiative. He explores stars and planets, and how life emerged on Earth, by specializing in the modes of interaction between light and matter, and the uses of remote sensing. His research focuses on understanding the origins of life through these scientific approaches, contributing to the broader field of astrobiology and planetary science.

Research topics

• Computer Science
• Physics
• Mathematics
• Astronomy
• Mathematics education
• Psychology
• Multimedia
• Biology
• Combinatorics
• Astrophysics
• Astrobiology
• Chemistry

Selected publications

• The TESS Objects of Interest Catalog from the TESS Prime Mission

  The Astrophysical Journal Supplement Series · 2021 · 300 citations

  • Computer Science
  • Physics
  • Astronomy

  We present 2241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its 2 yr Prime Mission. We list these candidates in the TESS Objects of Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously known planets recovered by TESS observations. We describe the process used to identify TOIs, investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well suited for detailed follow-up observations. The TESS data products for the Prime Mission (sectors 1-26), including the TOI catalog, light curves, full-frame images, and target pixel files, are publicly available at the Mikulski Archive for Space Telescopes.

  DOI

• The origin of life as a planetary phenomenon

  Science Advances · 2020 · 207 citations

  1st authorCorresponding
  • Astrobiology
  • Biology
  • Physics

  We advocate an integrative approach between laboratory experiments in prebiotic chemistry and geologic, geochemical, and astrophysical observations to help assemble a robust chemical pathway to life that can be reproduced in the laboratory. The cyanosulfidic chemistry scenario described here was developed by such an integrative iterative process. We discuss how it maps onto evolving planetary surface environments on early Earth and Mars and the value of comparative planetary evolution. The results indicate that Mars can offer direct evidence for geochemical conditions similar to prebiotic Earth, whose early record has been erased. The Jezero crater is now the chosen landing site for NASA's Mars 2020 rover, making this an extraordinary opportunity for a breakthrough in understanding life's origins.

  DOI

• A Pair of TESS Planets Spanning the Radius Valley around the Nearby Mid-M Dwarf LTT 3780

  The Astronomical Journal · 2020 · 96 citations

  • Physics
  • Astrophysics
  • Astronomy

  Abstract We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, V = 13.07, K s = 8.204, R s = 0.374 R ⊙ , M s = 0.401 M ⊙ , d = 22 pc). The two planet candidates are identified in a single Transiting Exoplanet Survey Satellite sector and validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of P b = 0.77, P c = 12.25 days and sizes r p , b = 1.33 ± 0.07, r p , c = 2.30 ± 0.16 R ⊕ , the two planets span the radius valley in period–radius space around low-mass stars, thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial velocity measurements from the High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N, we measure planet masses of and M ⊕ , which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and core-powered mass-loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.

  PublisherOA PDFDOI

• Going over the cliff: MOOC dropout behavior at chapter transition

  Distance Education · 2020 · 40 citations

  • Computer Science
  • Mathematics education
  • Computer Science

  Participants’ engagement in massive online open courses (MOOCs) is highly irregular and self-directed. It is well known in the field of television media that substantial parts of the audience tend to drop out at major episodic, or seasonal, closures, which makes creating cliff-hangers a crucial strategy to retain viewers (Bakker, 1993; Cazani, 2016; Thompson, 2003). Could there be an analogous pattern in MOOCs—with an elevated probability of dropout at major chapter transitions? Applying disjoint survival analysis on a sample of 12,913 students in a popular astronomy MOOC that built participants’ cultural capital (hobbyist pursuits), we found a significant increase in dropout rates at chapter closures. Moreover, the latter the chapter closure was positioned in the course sequence, the higher the dropout rate became. We found this pattern replicated in a sample of 20,134 students in a popular computer science MOOC that introduced participants to programming.

  DOI

Recent grants

• EAGER: Defining the Role of UV light in Prebiotic Chemical Evolution: the Imidazolium Bridge in Non-enzymatic RNA Replication

  NSF · $300k · 2019–2021

Frequent coauthors

• D. B. Guenther

  240 shared

• R. Kuschnig

  University of Graz

  217 shared

• S. M. Ruciński

  216 shared

• W. W. Weiß

  214 shared

• A. F. J. Moffat

  Université de Montréal

  210 shared

• J. M. Matthews

  University of British Columbia

  202 shared

• David W. Latham

  181 shared

• Lars A. Buchhave

  163 shared

Labs

• SasselovPI

Education

• Ph.D., Astronomy

  Harvard University

  1995

• M.S., Astronomy

  Harvard University

  1991

• B.S., Physics

  University of Sofia

  1986

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• JoAnn E Mansonh-359
• Randy L. Bucknerh-268
• Edward Giovannuccih-267
• Kristen Andersonh-263