Because the ice giant planets Uranus and Neptune have similar masses, sizes, and distances from the Sun, scientists often thought they formed in a similar way. But the two planets also have many differences, indicating they might not be as similar as they seem at first blush.Instead, each ice giant could have experienced its own unique, traumatic event in its past, putting them on two different evolutionary tracks. And in order to create a more complete picture of how the early solar system formed, scientists need to know exactly how our outermost planets came to be.Now, a team of researchers has used computer simulations to show that collisions with large, rocky bodies could have led to the two planets’ diverging histories, possibly explaining their differences.
Frombork is a small town in northern Poland that lies just off the beaten tourist track. For the car-less visitor to reach the village means negotiating the local bus routes. But there’s a huge payoff. Frombork’s fortified red-brick cathedral complex is every bit as majestic as nearby Malbork Castle, and it has an added bonus for astronomy enthusiasts: Here, Nicolas Copernicus turned the universe upside down.Within Frombork’s massive walls, the astronomer settled down to write his treatise describing a heliocentric (Sun-centered) cosmos, eventually published as De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in 1543. To this day, the great thinker rests just beneath the cathedral floor.How should we think of Copernicus’ legacy, 476 years after his death? In some ways, he was a radical: His theory forced us to think of Earth as a ball of rock whizzing through space — a shocking idea at the time. But in other ways, he was conservative, imagining the planets moving in perfectly circular orbits, just as the ancient Greeks had believed some 14 centuries earlier. In fact, On the Revolutions was, in some respects, a “tweaking” of the Almagest, the book-length treatise on the structure of the cosmos written by the Greek thinker Ptolemy in the second century.
How a long-gone Apollo rocket returned to EarthAn amateur astronomer’s discovery kicked off a Space Age detective story.By Doug Adler | Published: Monday, May 11, 2020On September 3, 2002, amateur astronomer Bill Yeung discovered an object that he believed was a never-before-seen asteroid in a rapid orbit around Earth. While it’s easy for massive planets such as Jupiter to frequently capture objects like asteroids and comets, Earth is smaller and has less gravitational oomph with which to influence interplanetary passersby.Yeung’s discovery, formally named J002E3, became the focus of an intense analysis with a unique result. The object was not an asteroid captured by Earth in a cosmic game of coincidence. This was a relic of humanity’s space race: an Apollo-era rocket that had been placed in orbit around the Sun — and then returned to Earth.An unusual discoveryYeung was already well known in astronomy circles for his prolific discovery of other asteroids — J002E3 was simply one more to add to his collection. But astronomers at the Minor Planet Center quickly realized that J002E3 was not an asteroid. Its unusual orbit made some suspect that it was, in fact, human-made — a leftover piece of space hardware.But an analysis of recent launches did not identify any possible candidates for the source of the object. Scientists at the Jet Propulsion Laboratory (JPL) in Pasadena, California, tracing back the object’s trajectory, discovered that it had been captured in April 2002 into Earth orbit from an orbit around the Sun that was similar to Earth’s. Backtracking even further, the object appeared to have gotten into its Sun-circling orbit after originally escaping Earth orbit all the way back in February 1971.This gave researchers some potential clues as to the origin of J002E3.
The planets in our solar system formed from the solar nebula of gas and dust that surrounded our infant Sun. The material in this nebula was spinning; as the planets formed from this material, they, too, were spinning.Objects in motion will stay in motion unless an outside force acts on them. In most everyday applications on Earth, friction counteracts motion by slowing things down, so energy must be added to keep an object moving (or spinning). Our planet doesn’t slow down much simply because there is almost nothing stopping it from continuing to spin.But there are factors slowing it down, as well as speeding it up. The collision that formed the Moon added rotational energy to the planet, making Earth’s day only about five hours long. Over time, tides raised on Earth by gravitational interactions with the Moon and, to a much lesser extent, the Sun, have slowed our planet’s rotation to the 24-hour day we now experience. Current measurements show the effects of the Sun and Moon are slowing Earth’s rotation at a rate of about 2 milliseconds every 100 years.
The exploration of Pluto wasn’t easy, but it sure was worth it. As David Grinspoon and I recount in our book, Chasing New Horizons, it took 14 years (1989 to 2003), about a dozen different mission concept proposals, and the weight of the first National Academy Planetary Science Decadal Survey just to unleash the funding. After a fierce competition among rival teams, NASA ultimately selected New Horizons as its Pluto flyby mission.That was followed by a breakneck four-year schedule to design, build, and test the spacecraft in order to meet the time-critical 2006 launch window needed to use Jupiter for a gravity assist. Once that was achieved, New Horizons had to undertake the 9.5-year journey across our solar system to reach Pluto and its system of five moons. The entire effort took 26 years and the dedication of literally thousands of individuals, and was done entirely with no backup, no plan B, no Voyager 2 in case Voyager 1 failed.
The Moon keeps its familiar face pointed toward Earth, but there are two stable positions. It also would be stable if its farside faced our planet. At the present time, there are small impacts that must kick the Moon away from perfect orientation. When that happens, it oscillates about its stable orientation in two ways. The Moon can rock back and forth in the east-west direction. This oscillation takes 1,056 days, or 2.9 years. The lunar poles also can become unstable, causing a 75-year wobble. Earth’s poles experience a similar effect called Chandler wobble.The Moon also experiences tidal distortion from Earth’s gravitational pull.Giant basin-forming im-pacts could have reoriented the Moon early in its lifetime. Such large impacts would have left the Moon rocking by large amounts until the friction damped the motion. These basin-forming impacts happened when the Moon was much closer to Earth.
Friday, May 15Asteroids 23 Thalia and 40 Harmonia share a relatively small region of the sky this month. To see them tonight, find Virgo’s bright star Spica above the southern horizon after dark. Slide your gaze 15° east to 4th-magnitude Iota (ι) Virginis. Look 5° west of Iota, and you’re smack-dab in the middle of an imaginary line running southwest between Thalia and Harmonia. Tonight, the two are 2.2° apart, with Harmonia farther southwest than Thalia. Both of these main-belt asteroids are roughly 67 miles (108 kilometers) across. If you return to this region at the end of the month, you’ll find that Thalia has moved about 2° southwest, appearing to chase after Harmonia, which has slid roughly 2° due west.
The new season of Cosmos, which premieres tonight, demonstrates the remarkable stickiness of a great idea. In 1973—years before there was Cosmos the book and Cosmos the original television series—Carl Sagan wrote a book called The Cosmic Connection. It mixed cutting-edge astronomical discoveries with informed speculation, philosophical ruminations on the scientific method, and elements of personal memoir.It was a science book not quite like any that had been published before. Sagan subtitled it "An Extraterrestrial Perspective," and that is how it read. It was a deeply personal, quirky, passionate account told by someone whose mind had just returned from a journey far, far beyond Earth (billions and billions of miles away, you might say). I read it as a child and was captivated. I had lot of good company. The Cosmic Connection was a hit, Sagan ended up as a semi-regular guest on The Tonight Show, and for many people he became the definitive public face of science.The connection that began with that book remains unbroken. In 1980, The Cosmic Connection begat the Cosmos TV show on PBS, which has reportedly been seen by 500 million people around the world. Sagan died in 1996 but his voice returned in a 2014 sequel, Cosmos: A Spacetime Odyssey, again co-created by Sagan's widow Ann Druyan and now hosted by Neil deGrasse Tyson. I had some quibbles with the show's history, but enormous admiration for its message and its creativity.
Sunday, May 24Observers with larger scopes might want to use this time to search out the distant dwarf planet Pluto this morning. Rising higher with each hour after midnight, you’ll find the magnitude 14.7 world just 2.1° west of bright Jupiter, which is nearly magnitude –2.6. Farther east lies Saturn; the ringed world is roughly magnitude 0.5.
Just how big is the Andromeda galaxy?Astronomers used to believe that the Andromeda galaxy, our nearest galactic neighbor, was three times as massive as the Milky Way. Not anymore.
The length of a day on Venus keeps changingResearchers have spent decades trying to pin down exactly how long a day on Venus lasts. Finding the answer cuts to the core of fundamental mysteries about the planet.
This composite image of the cloud-covered planet Venus uses data from the Japanese probe Akatsuki.Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency