Dear readers,

It's perfectly fine that human beings want to travel in space. But we have to reckon with the fact that space doesn't want anything to do with us. The exterior environment of space, of course, represents instantaneous death, what with the killing cold and the absence of any atmosphere. But even inside a spacecraft or a space station—cozy, pressurized, temperature-controlled, with food supplies, comfortable sleep pods, and a zero-g privy to take care of unavoidable essentials—the body doesn't care for space.

Space radiation, which makes it through the walls of even the sturdiest ship, raises an astronaut's lifetime risk of cancer. Just as problematic are the effects of what would seem to be the happiest part of living off-planet: weightlessness. Retired astronaut Scott Kelly, who spent close to a year aboard the International Space Station (ISS) in 2015 and 2016, once told TIME that he's often asked whether the view or the absence of gravity is the best part of being in space. The view, he acknowledged, is magnificent, but it's also like having an artistic masterpiece hanging in your living room—eventually you'd quit noticing it. But you never get tired of the ability to fly.

That ability comes at a price, though. Without gravity, the immune system weakens, the bones decalcify, muscles grow slack, and the very shape of the eyeball changes, becoming less spherical. (The only upside, as Kelly reports, is that without having to support the weight of the body for extended periods, the soles of feet lose their callouses.)

But of all of the challenges the body faces during extended periods in zero-g, perhaps the worst is the hit that the heart takes, as a study out this week reveals. The research, published in the journal Circulation, took an unfamiliar approach to investigating cardiac health, comparing the effect Kelly's near-year in space had on his heart to similar changes experienced by endurance swimmer Benoit Lecomte, who swam 2,821 km (1,753 mi) from Japan to Hawaii from June to November 2018.

The two men had plenty in common. Kelly's 340 days in space outpaced Lecomte's 159 days in the water (he took breaks to rest and sleep aboard an escort sailboat), but both were marathoners. Both also exercised vigorously, with Kelly spending one to two hours every day working out and Lecomte spending six hours a day swimming. Most importantly, both experienced weightlessness, with Lecomte's time in the water considered a good proxy for authentic zero-g.

Both, too, paid a price for their heroics. As the study showed, Kelly lost an average of .74 gm (.026 oz.) in mass per week from his heart's left ventricle over the course of his time in space—almost identical to the .72 gm per week Lecomte lost. Both too lost mass in their heart's diastolic diameter, Kelly's falling from 5.3 cm to 4.6 cm and Lecomte's from 5 cm to 4.7 cm. Neither Kelly nor Lecomte had any change in the left ventricle ejection fraction, or the amount of blood pumped out with each contraction.

The study's implications are not all that troubling when it comes to long-distance swimmers since, well, how many people plan to butterfly stroke across the Pacific? But for a species that fancies itself a spacefaring one, the findings are bad news. ISS crew members follow a rigorous exercise regimen intended to counteract the effects of weightlessness. It helps: astronauts return home with stronger bones and more muscle mass than they would have if they spent their entire time aloft weightless and sedentary. The heart too can only benefit from from regular exercise—but clearly not enough.

There are, of course, technological solutions, like creating artificial, centrifugal gravity by rotating a spacecraft at the proper speed (see, e.g., The Martian and 2001: A Space Odyssey). But even our best and newest crewed spacecraft adhere to the capsule and habitation module model, with no great, rotating space liners even in the design pipeline. For now we remain newbies, novices, taking to space in our little pods without our gravity, and bringing our frail and fallible bodies with us. We're getting by—kind of—and we'll continue to. But even 60 years after Yuri Gagarin became the first human being in space, we still have an enormous amount of work to do before the cosmos become anything like a home. Earth—familiar as it may be, unglamorous as it may seem—remains our place in the cosmos.

—Jeffrey Kluger

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NASA stitched together 71 images the Perseverance rover took with two different cameras to create this selfie in front of Mount Mercou, a rock outcrop that stands 6 m (20 ft. high) in Mars' Jezero Crater.


And the winners of the first all-private trip to space are...

All that business about space travel's tolls on the human body doesn't mean a fig to people hoping to leave the planet. Just ask Sian Proctor and Chris Sembroski, who learned this week that they'll be heading for orbit as early as this fall as the final two members of Inspiration4, the first all-private space mission.

Inspiration4 is the brainchild of Jared Isaacman, a billionaire tech founder who recently purchased four seats aboard a SpaceX Crew Dragon spacecraft, in large part to raise funds and recognition for St. Jude Children's Research Hospital in Memphis, Tenn. Isaacman, 38, an accomplished pilot and aerobat, picked himself as commander, and knew he wanted at least one former St. Jude patient to accompany him. He selected Hayley Arcenaux, 29, who at age 10 was treated for bone cancer, with parts of her left leg being replaced by metal rods. As The New York Times reports, she will be the youngest American ever, and the first person with a prosthetic body part, to go to space.

Proctor, 51, and Sembroski, 41 were chosen via a contest Isaacman sponsored that required contestants to design an online store and share videos describing their space dreams. They also had to make a donation to St. Jude. Sembroski, a data engineer for Lockheed Martin, is a U.S. Air Force veteran, and Proctor, a community college professor, applied to NASA for astronaut training and made it down to a class of 47 finalists out of 3,500 applicants before she was cut.

X-rays are streaming from Uranus

O.K., stop snickering. It's true, for one thing—x-rays are streaming from the seventh planet from the sun. For another, you can pronounce it "YOR-uh-nus" if that helps. Many astronomers do, for precisely the obvious reason.

Now that that's out of the way, NASA this week announced that a new analysis of Uranus data collected in 2002 and 2017 revealed steady emissions of x-rays from the first dataset and curious pulses from the second. X-rays have been detected coming from Jupiter and Saturn, but less so from Uranus, and scientists have been at pains to explain what the new findings mean. The best guess is that the sun is responsible: just as the Earth reflects white solar light back into space, Jupiter and Saturn scatter x-rays. Uranus, another of the solar system's four gas giants, could be expected to do the same.

But there are other possible sources, too. Unlike the other seven planets, Uranus orbits on its side, with its north pole and south pole actually pointing east and west. It also has two fine rings which orbit around its sideways equator. Saturn's much bigger, more robust rings are known to produce x-rays when they're hit by charged particles from space; Uranus' rings could do likewise.

A third explanation could have to do with Uranus's cockeyed orientation. Not only does the planet rotate on its side, but the lines of its magnetic field, which should be sideways too, are actually at an angle offset from the planet's position. That, the astronomers suspect, could cause especially intense and complex auroras, and in turn produce x-ray emissions.

The planet hiding inside Earth

Some 4.5 billion years ago, a passing (and now extinct) planet known as Theia slammed into the primordial Earth, sending up a massive cloud of space debris and turning much of the Earth's surface into a roiling magma sea. The debris ultimately coalesced into our moon, and the impact contributed to the Earth's 23-degree tilt, which gives us our seasons. Only poor Theia suffered—or maybe not as much as we thought, because part of it may still be with us.

As Space.com explains, that's the theory behind a paper presented last week to the Lunar and Planetary Society by University of Arizona doctoral student Qian Yuan and his colleagues. Their work concerns two great masses of heavy rock that lie beneath Africa and the Pacific Ocean, informally known as "the blobs." They were thought to have been formed as the Earth's mantle cooled unevenly after the Theia impact, causing some mantle material to sink down toward Earth's core.

Yuan now proposes an alternate theory: Dense rocks from Theia would have been heavy enough to avoid getting ejected into space or settling into Earth's mantle. Instead, they fell towards the Earth's core, forming the blobs. Theia may have left a piece—or multiple pieces—of itself behind. "This crazy idea is at least possible," a decidedly humble Yuan told the journal Science.

Another flop for Starship

To hear Elon Musk tell it, his towering Starship spacecraft will carry a crew around the moon and back as early as 2023. And to see the Starships—stainless steel, towering 50 m high—is to believe they can do great things. They might, too, provided they can quit crashing.

March 30 marked the fourth test of a Starship prototype performing a relatively short hop into the sky in an attempt to test its upright, rocket-powered landing system. As Ars Technica reported, it was the fourth time the spaceship has wound up in pieces. Past attempts at least got close to sticking the landing, with the third of the four actually touching down successfully before blowing up 10 minutes later due to a fuel leak. This one didn't get nearly as close to succeeding.

After taking off and reaching its planned maximum altitude of 10 km, the rocket pitched over for a belly-first descent as it's supposed to, before igniting its engines to pitch back upright in preparation for landing. It was at that point that the rocket descended into a low Texas cloud bank—and at that point too explosions were heard. Moments later, nothing but debris descended through the bottom of the clouds. The rocket's remains landed precisely on the pad, allowing SpaceX boss Elon Musk an opportunity for some face-saving humor.

"At least the crater is in the right place!" he tweeted.

The good news for SpaceX is that they're building Starship prototypes at such a clip that one is rolling off the assembly line every two to three weeks. The bad news is that at this rate it looks like they'll need them all.

The ISS Experience

This week, TIME released Advance, the second episode of Space Explorers: The ISS Experience, a 3D virtual reality experience of life aboard the International Space Station, produced by TIME and Felix & Paul Studios. The episode premiered at SXSW 2021, and is now available in 360-mobile format through 5G carriers, virtual reality headsets on the Oculus Store and in select domes and planetariums. Click on the image below for a teaser.

Space Explorers: The ISS Experience episode two ADVANCE


TIME Space is written by Jeffrey Kluger, Editor at Large at TIME and the author of 10 books, including Apollo 13, Apollo 8, and the new space novel Holdout. Follow him at @jeffreykluger. It is edited by Alex Fitzpatrick.

We welcome any feedback at space@time.com.

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