Patience Rewarded with a Planet

Astronomers have collectively cataloged more than 5,000 planets beyond our Sun, a feat borne from the immense efforts of thousands of scientists. However, not all of these discoveries required the same amount of perseverance: while some planets neatly fell out of abundant high-quality data, other worlds required intensive analysis and years of additional study to earn their places in our archives. A recently discovered planet named TOI-2010 b falls firmly into the latter of these categories.

TESS and the Struggles of Single-Transit Planets

The majority of exoplanets discovered so far were initially flagged by space-based telescopes looking for the repeating dips in starlight caused by circling, intermittently photobombing planets. One of the most productive of these telescopes is NASA’s Transiting Exoplanet Survey Satellite, or TESS, which stares are one chunk of the sky for about a month before moving on to observe a new patch. This is a productive strategy that has netted thousands of exoplanet candidates across the whole sky, but it also lets some planets fall through the cracks. Astronomers need to observe more than one transit of a planet to nail down its period, and many of the most interesting cold planets take longer than a month to complete a lap around their star. Often, TESS catches only one transit of these worlds before it proceeds to the next area of the sky, leaving astronomers in a maddening predicament: they know an interesting planet is there, but they have no idea when it will transit again.

A number of astronomers have taken up the challenge of chasing down these “single-transit” planets, and recently a team led by Christopher Mann (University of Montréal) achieved a significant victory: the discovery and characterization of a Jupiter-like planet with a 141-day period.

Introducing: TOI-2010 b

Two side-by-side time series of a high-quality planetary transit.

Left: The first recorded transit of TOI-2010 b as seen by TESS. Right: Another TESS transit, caught after NEOSat refined the orbital period and late into the team’s analysis. Click to enlarge. [Mann et al. 2023]

Back in 2019, TESS captured a single, beautifully clear transit of a Jupiter-sized planet around a star named TOI-2010. Although only one transit could not uniquely determine the planet’s period, reconnaissance spectra and high-contrast imaging revealed a path forward: TOI-2010 was a good candidate for radial velocity follow-up. So, the team embarked on a three-year campaign to measure the planet’s period. Unfortunately, the resulting constraints were only strong enough to predict that the next transit could take place anytime within a week-long window. No Earth-bound telescope could monitor the sky uninterrupted for that long.

Enter the Near-Earth Object Surveillance Satellite (NEOSat), a suitcase-sized telescope launched and operated by the Canadian Space Agency and the Department of National Defence/Defence Research and Development Canada. In December of 2021, this satellite aimed its 15-cm telescope at TOI-2010 and didn’t look away for six straight days. It caught another transit of TOI-2010 b right near the middle of the predicted window, and in doing so ended the years of initial characterization. Astronomers finally had all of the parameters they needed to follow up the planet sometime in the future.

A two-panel plot of radial velocity amplitudes. The top plot shows a time series, while the lower plot shows the phase-folded measurements. The best-fitting model is plotted alongside the data in both plots.

The radial velocity measurements of TOI-2010, which reveal the tell-tale pattern of a circling planet. Click to enlarge. [Mann et al. 2023]

That information will likely be put to good use soon. As a relatively cold (and therefore rarely found) planet that circles a bright (and therefore easy to follow-up) star, it’s amenable to several different measurements including Doppler spectroscopy and infrared spectroscopy to target the planet’s emission. All of these exciting possibilities are only possible thanks to the determination and patience of this collaboration who made sure that this planet didn’t slip away.


“Giant Outer Transiting Exoplanet Mass (GOT ‘EM) Survey. III. Recovery and Confirmation of a Temperate, Mildly Eccentric, Single-transit Jupiter Orbiting TOI-2010,” Christopher R. Mann et al 2023 AJ 166 239. doi:10.3847/1538-3881/ad00bc