Readers react to cosmic smashups and tricky spacecraft landings

Science News January 30, 2021 cover

A smash hit

In “A complete collection of cosmic smashups” (SN: 1/30/21, p. 30), Emily Conover and Nadieh Bremer visualized every gravitational wave event spotted so far.

Freelance data visualization designer Nadieh Bremer “reduced an excruciatingly complex subject, gravitational waves produced by cosmic collisions, into a very interesting graphic. Emily Conover made it understandable,” reader Richard Polangin wrote. “Bravo to your very gifted staff!”

Reader Dave Proffitt noticed the colliding black holes were quite massive. “Why no detections in the [mass] range of commonly known black holes?”

It’s easier for the LIGO and Virgo observatories to spot more massive mergers because the gravitational waves are larger. “So, it’s true that there are a lot of detected events that were quite massive. However, there are a handful of detected events that involve quite small black holes,” Conover says. One detection, represented in the illustration by the small circle at about 1.6 billion years, resulted from the merger of a black hole with about 8.8 solar masses and a black hole with about five solar masses. “Three solar masses is the lower limit for what can be confidently called a black hole,” she says. “You can’t get smaller than that without it being difficult to d­etermine whether it’s a black hole or a neutron star.”

Left out

Scientists are getting inventive with ways to touch down on Earth’s neighbors, Lisa Grossman reported in “How to safely land on Venus or Europa” (SN: 1/30/21, p. 12).

Reader Michael Stebel was disappointed that the story did not mention the Huygens probe, which landed on Saturn’s moon Titan in 2005. “Although [the probe] sent back data and images for less than six hours, it was an incredible achievement … especially notable when one considers the distance involved, the extreme cold and the thick hazy atmosphere of Titan,” he wrote.