Lifeboat Foundation

The journey took a very long time—505 days to fly 26,000 miles (42,000 km) at an average speed of about 45 mph (70 kph)—but pilots Bertrand Piccard and Andre Borschberg successfully landed the Solar Impulse 2 aircraft in Abu Dhabi on Tuesday, after flying around the world using only the power of the Sun. Solar Impulse 2 is a solar-powered aircraft equipped with more than 17,000 solar cells that weighs only 2.4 tons with a wingspan of 235 ft (72 m). Technical challenges, poor flying conditions, and a delicate aircraft all contributed to the slow pace. Gathered here are images from the record-setting circumnavigation, undertaken to help focus the world’s efforts to develop renewable energy sources.

ZeroAvia’s hydrogen fuel cell could be a game-changer for aircraft of all sizes.

Moderna Therapeutics has just entered phase two of its clinical trials. Here’s how mRNA vaccines work and what the latest developments mean.

The standard formulation of quantum theory relies on a fixed space-time metric determining the localisation and causal order of events. In general relativity, the metric is influenced by matter, and is expected to become indefinite when matter behaves quantum mechanically. Here, we develop a framework to operationally define events and their localisation with respect to a quantum clock reference frame, also in the presence of gravitating quantum systems. We find that, when clocks interact gravitationally, the time localisability of events becomes relative, depending on the reference frame. This relativity ia a signature of an indefinite metric, where events can occur in an indefinite causal order. Even if the metric is indefinite, for any event we can find a reference frame where local quantum operations take their standard unitary dilation form. This form is preserved when changing clock reference frames, yielding physics covariant with respect to quantum reference frame transformations.

Lassina Zerbo, head of body monitoring test ban treaty, responds to White House discussions about potential first US test for 28 years.

Julian Borger in Washington.

TUNGUSKA: Giant skipping iron stone?

Scientists have a new explanation for an explosive cosmic event in 1908 that flattened trees for hundreds of miles in a remote Siberian forest.

This week at NASA:

🚀 Preparing to #LaunchAmerica 🛰️ JAXA’s spacecraft delivers cargo to the International Space Station 🕵️‍♂️ The detective capabilities of NASA’s Perseverance Mars Rover.

Like biological brains, artificial neural networks may depend on slow-wave sleep for learning.

Jupiter has captured an icy comet from the outer solar system in a bizarre orbit that will bring it back to within 3 million kilometers of the giant planet in 2063. The only Sun-orbiting objects known to come closer were the fragments of Comet Shoemaker-Levy 9, which plunged into the Jovian cloud deck in July 1994.

A year ago, NASA’s asteroid-hunting ATLAS project in Hawai’i discovered 2019 LD2, and further observations showed it was a comet. New observations this spring confirmed it as a periodic comet and placed its orbit near Jupiter, leading Larry Denneau (University of Hawaii) to announce May 20th that P/2019 LD2 was the first comet among the Trojans. This family of several thousand asteroids shares Jupiter’s orbit but stays steady at about 60° ahead or behind of the planet. The discovery of a comet among Trojan asteroids was surprising because most of them are thought to have been captured in the solar system’s early years — any ices ought to have evaporated long ago.

However, when amateur astronomer Sam Deen used software on the Jet Propulsion Laboratory’s solar-system dynamics website to calculate the object’s orbit, he found P/2019 LD2 recently had a close encounter with Jupiter that left its orbit unstable. The model showed that the comet had likely been a Centaur, part of a family of outer solar system asteroids, with an orbit reaching out to Saturn. Then, on February 17, 2017, it passed about 14 million kilometers from Jupiter, an encounter that sent the comet on a wild ride and inserted it into an odd Jupiter-like orbit.