Lazuli's Coronagraph Eyes 27 Giant Exoplanets in First Private Space Telescope Target List

A new paper posted to arxiv.org gives the first concrete answer to a question about the Lazuli Space Telescope: once it is in orbit, which planets will it look at first? The authors, Logan Pearce of the University of Michigan's Department of Astronomy and Ewan Douglas of the University of Arizona's Steward Observatory, propose a list of 27 targets. All of them are giant exoplanets.

Lazuli is billed as the first privately owned space telescope. It is the project of Eric Schmidt, Google's former CEO, and is scheduled to launch by 2029. Its mirror will span 3 meters, wider than the 2.4-meter mirror on Hubble. It will carry three instruments: a wide-field optical imager, an integral field spectrograph, and the ExtraSolar Coronagraph, or ESC. The paper concerns the third. It is titled "The first selection of optimal targets for the Lazuli ExtraSolar Coronagraph's reflected starlight exoplanet campaign."

The ESC is built around a different way of seeing planets. Every exoplanet imaged directly so far has been caught by its own glow, the thermal emission from leftover heat. That heat fades as a planet ages, so older planets grow dimmer and harder to find. The ESC will instead collect starlight bounced off a planet's atmosphere, and that signal does not decline with age. The authors say this opens the way to studying mature planetary systems. Working at visible and near-infrared wavelengths, roughly 0.5 to 2 microns, also lets the telescope resolve planets closer to their stars than thermal imaging allows. The authors add that such observations could probe for biosignatures.

The method has a steep cost. Planets seen in reflected light are faint against their stars, at contrasts of roughly one part in ten million to one part in a billion. Exposures would run from tens to hundreds of hours. For a telescope with a 3-meter mirror, the authors write, blind searches are impractical. Their answer is to choose planets whose orbits are already well measured, so observing time can be scheduled when a detection is most likely. That is why the list leans on known planets.

Some of the names will be familiar to anyone who follows the field. 55 Cancri d is a Jupiter analog. HD 181433 d travels a highly eccentric orbit and belongs to a system that also holds an ultra-short-period super-Earth. Beta Pictoris b was among the first exoplanets ever directly imaged, and it interacts with the star's well-known debris disk. Of the host stars, the paper's color-magnitude diagram shows only one is an M dwarf.

The authors say the list covers ages and temperatures that direct imaging has not reached before, pushing into colder gas giants than any imaged so far. Some targets also fall within reach of other facilities: the thermal imager METIS on the Extremely Large Telescope, and the coronagraphic instrument on the Nancy Grace Roman Space Telescope. Overlapping observations, they argue, would give a more comprehensive characterization of those atmospheres.

The article closes with a note of caution about the novelty of the venture. A privately owned space telescope has no precedent, and how well it performs is unknown. So is what private ownership will mean in practice, whether it makes the work more efficient, introduces unforeseen problems, or both. What will count in the end, the piece says, is what Lazuli contributes to exoplanet science, and that test is still a few years off.