Publications

Since 2010, I have worked on eleven projects resulting in peer-reviewed publications: five first-author papers, five papers in which I was a co-author, and one workshop proceedings for which I was the rapporteur. All eleven are given below with short summaries and links to where you may download an open-source PDF of the publication.


First Author Publications

SearchingForLife2.jpg

Searching for Life Across Space and Time: Proceedings of a Workshop

Rapporteur: Joseph R. Schmitt
Published September 14, 2017

The search for life is one of the most active fields in space science and involves a wide variety of scientific disciplines, including planetary science, astronomy and astrophysics, chemistry, biology, chemistry, and geoscience. The possibilities of alien life are vast: from life similar to Earth's own  to organisms that may not even be carbon-based. Scientists are looking both within the solar system, particularly Mars, Europa, and Enceladus, and to the exoplanets beyond, where new worlds are being discovered almost daily.

In December 2016, the Space Studies Board hosted a workshop to explore the possibility of habitable environments in the solar system and in exoplanets, techniques for detecting life, and the instrumentation used. This publication summarizes the presentations and discussions from the workshop.

Links: Download at The National Academies Press.


An artist’s rendering of Kepler-150 f (illustration by Michael S. Helfenbein).

An artist’s rendering of Kepler-150 f (illustration by Michael S. Helfenbein).

A Search for Lost Planets in the Kepler Multi-planet Systems and the Discovery of the Long-period, Neptune-sized Exoplanet Kepler-150 f

Authors: Joseph R. Schmitt, Jon M. Jenkins, and Debra A. Fischer
Published March 28, 2017

The Kepler space telescope has discovered thousands of planets, including many stars with multiple planets. In systems with many planets, it can be very difficult to discover long-period planets, which are already difficult to find, due to the noise caused by the other planets. In this paper, I examined the stars with three or more known planets, modeled their orbits, and removed their signals. Hidden in all that noise, I discovered a new signal. Using a variety of statistical techniques, I confirmed the new signal as the exoplanet Kepler-150 f, the fifth planet in the system. Kepler-150 f is approximately the size of Neptune and orbits its star in the habitable zone once every 637 days. It lies about 3,000 light years from Earth.

Links: The Astronomical Journal, ADS, arXiv, PDF, and PDF (small).

Sample news coverage: Yale News, Astronomy.com, Gizmodo, and The Indian Express.


High-resolution images of six stars with neighboring stars.

High-resolution images of six stars with neighboring stars.

Planet Hunters. X. Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission

Authors: Joseph R. Schmitt and 24 others
Published May 27, 2016

In this paper, we observed 75 stars believed to either host planets or be a closely-orbiting pair of stars. Target stars were selected exclusively by volunteers from the citizen science project Planet Hunters. This crowd-sourcing project lets users online look at real Kepler data to conduct their own search for exoplanets and other interesting phenomena. Among the 75 target stars, 10 are newly discovered hosts to planet candidates. The are likely to be true planets, but have not quite met the high statistical standard in order to be declared confirmed. We used two telescopes, the Southern Astrophysical Research (SOAR) telescope in Chile and the Keck II telescope in Hawaii, to perform high-resolution imaging of our target stars. Our observations found that at least 9 of our 75 stars had a neighboring star in its vicinity, 6 of them newly discovered, including one planet candidate host star. This high-resolution data will be useful in future planet vetting and studies concerning the number of stars in planet and eclipsing binary systems.

Links: The Astronomical Journal, ADS, arXiv, and PDF.


Quality of fit for four different models for many stars. Blue is good; red is bad.

Quality of fit for four different models for many stars. Blue is good; red is bad.

Modeling the Asteroseismic Surface Term Across the HR Diagram

Authors: Joseph R. Schmitt and Sarbani Basu
Published July 27, 2015

Astronomers have always been unable to accurately and precisely measure the masses, radii, ages, and other important properties of many stars. Asteroseismology is a new and powerful tool that has finally allowed astronomers to overcome this problem. Astronomers use asteroseismology to measure the frequencies at which stars pulsate. In theory, the measured pulsation frequencies of stars could be matched to the pulsation frequencies of computer models of stars. This would allow astronomers to match real observations of a star with unknown properties to a computer model of a star with known properties in order to calculate the real properties of the star. However, imperfections in the computer modeling of stellar surfaces lead to errors known as the "surface term".  This surface term must be corrected for in order to get the real stellar properties. In this paper, we created computer simulations of these surface terms for many stars with a variety of stellar properties and ages to explore how best to correct for this surface term for a wide variety of stars. We conclusively found that the surface term correction model proposed by Ball & Gizon (2014) works much better than other correction models for nearly all simulated stars in our study. This leads us to recommend the Ball & Gizon (2014) model for future asteroseismic analyses.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.


Illustration by Michael S. Helfenbein.

Illustration by Michael S. Helfenbein.

Planet Hunters. VII. Discovery of a New Low-mass, Low-density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)

Authors: Joseph R. Schmitt and 20 others
Published October 28, 2014

The Kepler space telescope stared at more than 150,000 stars for four straight years looking for the rare moments when an exoplanet, a planet beyond our solar system, would cross in front of its star. Most planets have perfectly periodic orbits. They show up at exactly the same time every time. However, if multiple planets orbit the same star, gravitational interactions between the planets can disrupt their perfect orbits. Planet Hunters, a citizen science project where volunteers online look at real data to help find exoplanets, found such a planet. A Planet Hunters user found an additional signal in the PH3 (or Kepler-289) system, which already had two known planets. However, instead of a perfectly periodic orbit, the new planet's orbit changed by as much as 10 hours over the course of a few orbits, a staggering amount. This allowed us measure the mass of the planet to be 4.0 times the mass of Earth, confirming the signal as a planet called PH3 c. With a radius 2.7 times that of Earth, PH3 c has a large atmosphere of hydrogen and helium, unusual for a planet of such low mass. PH3 c has been added to the ranks of the new class of low-mass, low-density planets whose existence have yet to be adequately explained..

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Sample news coverage: Yale News, Astronomy.com, and Sci-News.


An orbital representation of the KOI-351 system.

An orbital representation of the KOI-351 system.

Planet Hunters. VI. An Independent Characterization of KOI-351 and Several Long Period Planet Candidates from the Kepler Archival Data

Authors: Joseph R. Schmitt and 32 others
Published June 26, 2014

NASA's Kepler space telescope has now discovered thousands of planets, mostly with the aid of complex computer algorithms. However, some planets can escape the computer's sight, especially those with long orbital periods, those in systems with many planets, or those that do not orbit in a perfectly periodic manner. Planet Hunters is a citizen science project designed to find these missed planets. Planet Hunters shows real Kepler data to volunteers online to look for the characteristic dip in a star's brightness as a planet crosses in front of it. With their help, we discovered 14 new planet candidates that the computers had missed, including many with very long orbital periods. Half of new planet candidates orbit in their host star's habitable zone. One of these 14 planet candidates resides in the KOI-351 system, which already had six known planets. The new planet candidate has both a long(ish) orbital period and an extremely variable orbit, one time showing up 24 hours later than expected due to gravitational interactions with other planets in the system. At the time, our newly discovered planet candidate made KOI-351 the star with the most known planet candidates outside of our solar system at seven. Kepler-90, as it's called today, now has eight confirmed planets, tying our solar system for the the most planets known to orbit a single star.

Links: The Astronomical Journal, ADS, arXiv, and PDF.

Sample news coverage: BBC, Sky and Telescope,



Contributing Author

An artist's rendering of a possible solution to the KIC 8462852 mystery: a large family a comets.

An artist's rendering of a possible solution to the KIC 8462852 mystery: a large family a comets.

Planet Hunters IX. KIC 8462852 - where's the flux?

Authors: Tabetha S. Boyajian and 48 others, including Joseph R. Schmitt
Published January 27, 2016

Called "The Most Mysterious Star in the Galaxy" by The Atlantic due to speculation that the star KIC 8462852 might be host to an "alien megastructure", an idea explored by a separate, follow-up paper, our original paper made no references to aliens. Instead, our team, led by Dr. Boyajian, explored a series of natural explanations for the star's chaotic series of dips in the star's brightness. These dips in brightness have never been seen before and at times block up to 40% of the star's light. With no discernible pattern and no other example ever observed, we examined a variety of explanations, including a catastrophic collision between two planets, a series of collisions between large asteroids, a huge family of comets, and others. While none of these scenarios were very satisfactory, the best explanation of the set was the family of comets whose massive comas were obscuring a varying amount of the star as the family of comets passed across the star.

Links: Monthly Notices of the Royal Astronomical Society, ADS, arXiv, and PDF.

Sample news coverage: CNN, CBS News, NBC News, Newsweek, Bloomberg, and The Guardian.


Twelve new planet candidates transiting their host stars.

Twelve new planet candidates transiting their host stars.

Planet Hunters. VIII. Characterization of 41 Long-period Exoplanet Candidates from Kepler Archival Data

Authors: Ji Wang, Debra A. Fischer, Thomas Barclay, Alyssa Picard, Bo Ma, Brendan Bowler, Joseph R. Schmitt, and 26 others
Published December 18, 2015

The Kepler space telescope is the most prolific planet discoverer to date. For four straight years, it stared at more than 150,000 stars in the hopes of catching some of them blinking as planets crossed in front of them. Planets transiting in front of their stars block out some of the starlight, which is observed by the telescope as small dips in brightness. Computer algorithms are great at catching these transits when they happen repeatedly and perfectly periodically. However, computers struggle when there are only one or two transits visible (usually because the planets have very long orbital periods that are longer or approximately equal to the four years Kepler stared at it). Long-period planets are particularly interesting because they may reside in or just beyond their star's habitable zone. To date, few planets have been discovered just beyond their star's habitable zone. In order to find these long-period planets, the Planet Hunters citizen science project lets volunteers online search for these dips in brightness themselves. They made the initial discoveries of the 41 long-period planet candidates, most of which Dr. Wang then observed with the Keck II and Palomar 200-inch telescopes. Using statistical techniques, we verified that 7 of the 41 planet candidates are confirmed to high confidence, valuable additions to the family of long-period exoplanets.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.


An eclipsing binary with both a primary and secondary transit.

An eclipsing binary with both a primary and secondary transit.

Kepler eclipsing binary stars - VI. Identification of eclipsing binaries in the K2 Campaign 0 data set

Authors: Daryll M. LaCourse and 17 others, including Joseph R. Schmitt
Published August 5, 2015

After suffering a malfunction in one of its steering components, the NASA's Kepler space telescope began a new phase of its mission, K2, where the telescope would observe a different patch of sky every three months. A group of amateur astronomers led by Daryll LaCourse examined the first three months of data from the K2 extended mission to search for eclipsing binaries, pairs of star orbiting each other in which one or both stars cross in front of the other, blocking some of their starlight. Characterizing the population of eclipsing binaries helps astronomers learn the environment in which stars form. Eclipsing binaries are also one of the most common false positives when searching for exoplanets. Using techniques they learned and built from their work on the citizen science project Planet Hunters, the team found 207 eclipsing binaries, including 97 new discoveries. In a serendipitous discovery, the team also found two exoplanet candidates. Daryll LaCourse won the American Astronomical Society's Chambliss Amateur Achievement Award for this study.

Links: Monthly Notices of the Royal Astronomical Society, ADS, arXiv, and PDF.


Artist's impression of the view from a moon around planet PH2 b (credit: Haven Giguere).

Artist's impression of the view from a moon around planet PH2 b (credit: Haven Giguere).

Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data

Authors: Ji Wang and 21 others, including Joseph R. Schmitt
Published September 19, 2013

Thousands of exoplanets planets, planets beyond the solar system, have been discovered thus far. The majority of them have been found using NASA's Kepler space telescope. Kepler, launched in 2009, stared at the same patch of sky for four straight years looking for planets crossing in front of their host stars. These "transits" cause the brightness of the stars to dip as the planet blocks some of its starlight. While computers are excellent at finding the vast majority of these planets, some are missed, typically those with long orbital periods or those with a slightly variable orbital period. The Planet Hunters citizen science project excels at finding these missed planets. Volunteers can look at real data online to discover planets with their own eyes. In this paper, Planet Hunters volunteers found 43 planet candidates and forwarded them to the science team for vetting. Dr. Wang led the team in the confirmation of one of these 43 planet candidates, a Jupiter-sized exoplanet named PH2 b in the habitable zone of its host star.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.

Sample news coverage: Yale News, Space.com, The Independent, Universe Today, and Sci-News.


The observed X-ray luminosity was more than the predictions of two different models.

The observed X-ray luminosity was more than the predictions of two different models.

X-rays from Blue Compact Dwarf Galaxies

Authors: Philip Kaaret, Joseph Schmitt, and Mark Gorski
Published October 10, 2011

Blue compact dwarf galaxies are small galaxies with many clusters of blue stars. These stars are massive, hot, and short-lived. Stars that are at least 8 times more massive than the Sun live for a few million to a few tens of million of years until they die in a fiery explosion called a supernova. The result of most (or all) of these supernovae are either neutron stars, which are very dense stars a few miles across almost entirely composed of neutrons, or black holes, which are a more mysterious class of objects with such strong gravity near their cores that not even light can escape. A star orbiting a neutron star or a black hole can lose material to it. As the material falls towards the neutron star or black hole, it can reach such high temperatures that they emit X-ray radiation. These systems are called X-ray binaries. Because X-ray binaries are more likely to form soon after the neutron star or black hole forms, and because the stars that turn into neutrons stars or black holes had such short lives, the number of X-ray binaries and their total X-ray brightness can be used to measure the rate at which new stars are forming in that galaxy. In this study. Dr. Kaaret led our group in observing these galaxies with the Chandra X-ray Observatory. We discovered several X-ray binaries and compared their number and brightness to other measurements of the galaxies' star formation rates. We found that blue compact dwarfs have many more X-ray binaries and much more total X-ray brightness from X-ray binaries than typical galaxies. Because blue compact dwarf galaxies are similar to galaxies in the early universe, this implies that X-ray binaries might have had a larger effect than previously thought in heating the early universe.

Links: The Astrophysical Journal, ADS, arXiv, and PDF.