Confirmed: Voyager 2 Finally Reaches Interstellar Space, 42 Years After Its Launch

In 2012, Voyager 1 became the first human-made object to venture beyond our solar system. The space probe is no longer alone in that distinction. Today—November 4, 2019—researchers at the University of Iowa confirmed that Voyager 2 has entered interstellar space after starting its journey from Earth 42 years ago.

Voyager 2 has made history many times since its 1977 launch. It's been to Saturn and Jupiter, and it remains only spacecraft that has explored Uranus and Neptune. After exhausting the outer reaches of our solar system, Voyager 2's next destination became the mysterious regions of space that lie beyond it.

A new study from the University of Iowa published in the journal Nature Astronomy confirms that Voyager 2 left the realm of our sun on November 5, 2018. The point where our solar system ends and interstellar space begins may seem hard to define, but the Voyager crafts have provided scientists with a clear answer.

Rather than gradually transitioning from one type of space to another, our solar system has a physical boundary. The sun gives off a "solar wind" that's hot and low in plasma. This solar wind creates a bubble, called the heliosphere, that stretches billions of miles from the sun. On the other side of this bubble, space is much cooler and more dense in plasma. There's a clear point where the bubble ends, like what you'd see with a bubble of oil in a glass of water.

About a year ago, a plasma-wave instrument aboard Voyager 2 recorded a dramatic jump in plasma density, indicating that it had crossed over from the heliosphere into interstellar space. It made the transition about 11.1 billion miles from the sun, which is roughly the same distance Voyager 1 clocked when it entered interstellar space from a different point in the solar system.

"It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed," study co-author Bill Kurth said in a news release. "That says that these two points on the surface are almost at the same distance."

Co-author Don Gurnett added, "There's almost a spherical front to this. It's like a blunt bullet."

Now that both Voyagers are in the part of space that lies between the stars, they will orbit the galaxy for 5 billion years or longer. Scientists predict they will outlast Earth.

The Leonid Meteor Shower Peaks This Weekend—Here's the Best Way to Watch It

mdesigner125/iStock via Getty Images
mdesigner125/iStock via Getty Images

We're nearing the end of 2019, but there are still a few astronomical events to catch before the year is s out. This Sunday—November 17—the Leonid meteor shower is expected to peak. Here's everything you need to know before viewing the spectacle.

What is the Leonid meteor shower?

Like all meteor showers, the Leonids are caused by meteoroids from outer space burning up on their descent toward Earth. These particular shooting stars come from the rocky tail of Comet 55P/Tempel-Tuttle. Each November, debris from the comet pummels the Earth's atmosphere, causing meteors to light up the sky at rates that can exceed 1000 per hour.

The Leonids won't reach that frequency this year. According to EarthSky, the meteors would peak at a rate of around 10 to 15 per hour in a dark, moonless sky. But because the moon will be bright this weekend, sky-gazers will likely see less of them, with only the brightest shooting stars shining through.

How to See the Leonids

For your best chance of spotting the Leonids, look up the night of Sunday, November 17 and early in the morning of Monday, November 18. The shower reaches its peak after midnight. The moon will be in its waning gibbous phase at that time, so even with clear skies, viewing conditions won't be ideal. But there are ways to increase your chances of seeing as many meteors as possible. Try finding a large object to stand under—such as a tree or building—that will block your view of the moon. If you don't see anything right away, be patient: The more time you give your eyes to adjust to the darkness, the more likely you are to spot a shooting star.

What is Mercury in Retrograde, and Why Do We Blame Things On It?

NASA
NASA

Crashed computers, missed flights, tensions in your workplace—a person who subscribes to astrology would tell you to expect all this chaos and more when Mercury starts retrograding. For the remainder of 2019, that means October 31-November 20. But according to an astronomer, this common celestial phenomenon is no reason to stay cooped up at home for weeks at a time.

"We don't know of any physical mechanism that would cause things like power outages or personality changes in people," Dr. Mark Hammergren, an astronomer at Chicago's Adler Planetarium, tells Mental Floss. So if Mercury doesn’t throw business dealings and relationships out of whack when it appears to change direction in the sky, why are so many people convinced that it does?

The History of "Mercury in Retrograde"

Mercury retrograde—as it's technically called—was being written about in astrology circles as far back as the mid-18th century. The event was noted in British agricultural almanacs of the time, which farmers would read to sync their planting schedules to the patterns of the stars. During the spiritualism craze of the Victorian era, interest in astrology boomed, with many believing that the stars affected the Earth in a variety of (often inconvenient) ways. Late 19th-century publications like The Astrologer’s Magazine and The Science of the Stars connected Mercury retrograde with heavy rainfall. Characterizations of the happening as an "ill omen" also appeared in a handful of articles during that period, but its association with outright disaster wasn’t as prevalent then as it is today.

While other spiritualist hobbies like séances and crystal gazing gradually faded, astrology grew even more popular. By the 1970s, horoscopes were a newspaper mainstay and Mercury retrograde was a recurring player. Because the Roman god Mercury was said to govern travel, commerce, financial wealth, and communication, in astrological circles, Mercury the planet became linked to those matters as well.

"Don’t start anything when Mercury is retrograde," an April 1979 issue of The Baltimore Sun instructed its readers. "A large communications organization notes that magnetic storms, disrupting messages, are prolonged when Mercury appears to be going backwards. Mercury, of course, is the planet associated with communication." The power attributed to the event has become so overblown that today it's blamed for everything from digestive problems to broken washing machines.

What is Mercury in Retrograde?

Though hysteria around Mercury retrograde is stronger than ever, there's still zero evidence that it's something we should worry about. Even the flimsiest explanations, like the idea that the gravitational pull from Mercury influences the water in our bodies in the same way that the moon controls the tides, are easily deflated by science. "A car 20 feet away from you will exert a stronger pull of gravity than the planet Mercury does," Dr. Hammergren says.

To understand how little Mercury retrograde impacts life on Earth, it helps to learn the physical process behind the phenomenon. When the planet nearest to the sun is retrograde, it appears to move "backwards" (east to west rather than west to east) across the sky. This apparent reversal in Mercury's orbit is actually just an illusion to the people viewing it from Earth. Picture Mercury and Earth circling the sun like cars on a racetrack. A year on Mercury is shorter than a year on Earth (88 Earth days compared to 365), which means Mercury experiences four years in the time it takes us to finish one solar loop.

When the planets are next to one another on the same side of the sun, Mercury looks like it's moving east to those of us on Earth. But when Mercury overtakes Earth and continues its orbit, its straight trajectory seems to change course. According to Dr. Hammergren, it's just a trick of perspective. "Same thing if you were passing a car on a highway, maybe going a little bit faster than they are," he says. "They're not really going backwards, they just appear to be going backwards relative to your motion."

Embedded from GIFY

Earth's orbit isn't identical to that of any other planet in the solar system, which means that all the planets appear to move backwards at varying points in time. Planets farther from the sun than Earth have even more noticeable retrograde patterns because they're visible at night. But thanks to astrology, it's Mercury's retrograde motion that incites dread every few months.

Dr. Hammergren blames the superstition attached to Mercury, and astrology as a whole, on confirmation bias: "[Believers] will say, 'Aha! See, there's a shake-up in my workplace because Mercury's retrograde.'" He urges people to review the past year and see if the periods of their lives when Mercury was retrograde were especially catastrophic. They'll likely find that misinterpreted messages and technical problems are fairly common throughout the year. But as Dr. Hammergren says, when things go wrong and Mercury isn't retrograde, "we don't get that hashtag. It's called Monday."

This piece originally ran in 2018.

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