Astronomers Make It Rain, Search for Gin and Vampires

Astronomers are murmuring over a handful of envelope-pushing results announced without pomp yesterday on the open-access server arXiv.org. The studies, covering a variety of topics, carry far-reaching implications for our exploration of exoplanets and exoplanet-like signals, as well as the elusive but long-suspected tie between observers and Earth itself.

Among the papers is an intriguing report by Michael Lund (Caltech), who found a curious connection between himself and rain. Scientists have long sought anthropogenic catalysts for precipitation, and the history of stimulating rainfall has a checkered history.

But Lund says he can make it rain simply by trying to observe. Of the 17 nights he attempted to use the 200-inch Hale Telescope at Palomar Observatory in southern California over the past year, 15 were wet. Suspicious, he tallied weather data for Mount Palomar over a 12-month period and compared the results. He found that his observing runs suffered from four times the median number of rainy days and a whopping 350% the expected rainfall.

This curious superpower puts Lund in a unique position, he writes in the April Acta Prima Aprilia. Many of the world’s premier professional telescopes are in drought-stricken areas, from the Canary Islands and Chile to Australia, which earlier this year was hit by devasting fires. Astronomers could alleviate these regions’ dry spells by assigning Lund time on local telescopes — the more time, the better.

Vampire Transits

Joining Lund in the yearly custom of publishing cutting-edge results on the first day of April is a separate work by Maximilian Günther and David Berardo (both at MIT), who searched heaps of data for the telltale blip in a star’s light when a space vampire passes across its face.

“It is a truth universally acknowledged,” they write, “that a single human in possession of a good space telescope, must be in search of a space vampire.” This quest has become especially urgent in the last couple of decades, they add, as scientists have increasing suspected that vampires are not native to Earth.

The team created templates of what a bat- and a humanoid-shape vampire would look like to a telescope during a transit. Then they sorted through small, cool red dwarf stars observed by the Transiting Exo-Vampire Survey Satellite (TE_vSS), a space observatory equipped with refractors, which should be sensitive to space vampires because, unlike reflectors, they use lenses instead of mirrors. In addition to these stars’ size and dimness — which makes spotting a transiting object easier — red dwarfs also emit most of their emission at infrared wavelengths, which don’t dissociate vampire molecules the way shorter-wavelength light from our Sun does.

Of the stars studied, between 0 and 394 million show signs of space vampires in orbit, Günther and Berardo write. Unfortunately, it’s impossible to say with certainty which shape (bat or humanoid) the majority of these objects take, or whether they’re merely noise in the data — the authors note with chagrin that the signal they seek is some quadrillion times weaker than gunk in the data.

The Hunt for Habitable Worlds

But the study that may have the greatest long-term impact on astronomers’ future studies is that by Marven Pedbost (Earth), Chris Lintott (University of Oxford, UK), and colleagues. Ever since the first planet was discovered around a star other than our own, astronomers have searched with gusto for habitable worlds. To narrow the playing field, they’ve focused on exoplanets that, if they have Earth-like compositions, receive enough light from their suns to sustain liquid surface water. The region around a star where liquid water would survive is the habitable zone.

But Pedbost’s team says the community ought to focus on exoplanets that are worth living on. These worlds lie in a star’s really habitable zone, defined as “the region around a star where acceptable gins and tonic are likely to be abundant.” (The authors include non-alcoholic gins, for those of us who don’t like to tipple.)

The astronomers looked at the conditions required for juniper (a common botanical flavor in gin) and citrus cultivation. These they combined with a range of planetary conditions and parameters chosen “according to our whims” to determine the subset of attractive exoplanets.

The list is distressingly short, as the plot above shows. For example, only one of the seven exoplanets in the Trappist-1 system makes the cut.

Based on the unique properties of the quinine in tonic, which fluoresces at a wavelength of 460 nm when exposed to ultraviolet radiation, the team suggests that the proposed LUVOIR space telescope could detect really habitable exoplanets. But the James Webb Space Telescope, ostensibly set to launch in 2021, may also detect key chemical fingerprints in the exoplanets’ light. “We suggest that planets in the Really Habitable Zone be early targets for the JWST,” the authors write, “because by the time that thing finally launches we’re all going to need a drink.”

References:

Michael Lund. “Making It Rain: How Giving Me Telescope Time Can Reduce Drought.” Posted to arXiv.org April 1, 2020.

Maximilian Günther and David Berardo. “Searching for Space Vampires with TEvSS.” Posted to arXiv.org April 1, 2020.

Marven Pedbost et al. “Defining the Really Habitable Zone.” Posted to arXiv.org April 1, 2020.