We Reach Pluto Tomorrow! 10 Fast Facts About 'New Horizons'

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Tomorrow morning, July 14, at 7:49 am ET, the spacecraft New Horizons makes its closest approach to Pluto in history. We'll be nearer to Pluto than New York City is to Hong Kong. Over the coming months the spacecraft will return libraries of knowledge about the mysterious planet. Here are a few things you might not know about the extraordinary probe.

1. New Horizons is the fastest spacecraft ever launched.

In 2006, an Atlas V rocket blasted New Horizons into space. By its third separation stage, the spacecraft was traveling a shade under 10 miles per second. To give some idea of its speed, it took the Apollo astronauts three days to get to the moon. New Horizons reached the same distance in nine hours.

2. Jupiter’s gravity acted as a slingshot on the probe.

A “gravity assist” involves a spacecraft flying near a planet and using that planet’s gravity to change speed or direction, as if flung by a giant slingshot. Jupiter’s gravity hurled New Horizons an extra 9,000 miles per hour, ramping up its speed to 52,000 miles per hour. While traveling through the Jovian system, New Horizons gave its instruments a test run, capturing such never-before-seen phenomena as lightning near Jupiter’s poles.

3. It is carrying the ashes of the man who discovered Pluto.

In 1930, Clyde Tombaugh, an American astronomer at the Lowell Observatory, discovered the planet that was eventually named Pluto. Tombaugh died in 1997, and New Horizons is carrying a small amount of his ashes. When the probe eventually moves beyond the Kuiper Belt, Tombaugh's ashes will be the first to travel beyond our solar system. The probe also carries a CD-ROM containing the names of 434,000 people who signed up to have their names sent to Pluto.

4. Planetary scientists consider Pluto a “science wonderland.”

That’s how the team at Johns Hopkins University’s Applied Physics Laboratory, which operates the New Horizons mission for NASA, describes the Pluto system. In addition to mapping Pluto’s geology and morphology, and analyzing its atmosphere and weather, New Horizons will study Charon, Pluto’s largest moon. By orbiting around a common center of gravity, the two worlds make up the only “binary planet” in the solar system. This is the first time we can study a new planetary class known as “ice dwarf” (the other two in our solar system being terrestrial planets and gas giants).

5. The entire mission will use less power than two 100-watt bulbs.

The energy efficient spacecraft is powered by a radioisotope thermoelectric generator (RTG), a kind of plutonium power plant. Like a big thermos bottle, the spacecraft is wrapped in thermal blankets (the gold foil seen in photographs) to hold in the heat produced by the spacecraft’s electronics, keeping them at a stable temperature. Notably, the RTG doesn’t provide propulsion. The spacecraft is still flying on the speed created by the launch and Jupiter’s gravity assist.

6. Its data is transmitted to Earth at 2 kbps.

The spacecraft uses a giant dish antenna to communicate with NASA’s Deep Space Network. It’s no trivial effort, though; the beam is only 0.3-degrees wide and has to hit Earth from Pluto and, eventually, beyond. (Considering the distances involved, New Horizons is quite the sharpshooter.) It takes four hours for data to arrive at the spacecraft, and once the flyby is complete, the probe will need a full 16 months to send all the data home.

7. There is almost zero margin for error.

The numbers are astonishing: New Horizons has traveled 3 billion miles at approximately 31,000 miles per hour (currently) and, if all goes as planned, will hit a target just 200 miles across. Because of orbital mechanics, if it is 100 seconds off course, it will not be able to gather 100 percent of the desired scientific data. Think about that: 100 seconds off course from a travel time of 9.5 years. Now that’s precision.

8. New moons mean new dangers.

In 2011, New Horizons discovered a second moon orbiting Pluto (Kerberos), and a year later a third (Styx). That’s been both exciting and worrying. These moons lack the mass and gravity to keep debris caused by planetary collisions from flying into space, where they could potentially smash into New Horizons. Debris doesn’t have to be big to be a threat: a piece the size of a grain of rice could prove catastrophic to the probe. Think of a rock hitting your windshield. Now imagine if you were driving 31,000 miles per hour.

9. The USA is the first country to explore every planet in the solar system.

NASA has been the first to launch each spacecraft that has successfully visited every planet, starting with Mariner 2 in 1962. July 14 is also the 50th anniversary of the Mariner 4 mission to Mars, the first exploration of the red planet. New Horizons completes humanity’s reconnaissance of the classical solar system.

10. The New Horizons mission does not stop with Pluto.

Once the spacecraft passes Pluto, it will have enough power and propellant to continue into the Kuiper Belt, a gigantic zone of icy bodies and mysterious small objects orbiting beyond Neptune. These objects are the building blocks of Pluto and planets like it. The new course will take New Horizons one billion miles beyond Pluto.

Does Sound Travel Faster or Slower in Space?


Viktor T. Toth:

It is often said that sound doesn’t travel in space. And it is true … in empty space. Sound is pressure waves, that is, propagating changes in pressure. In the absence of pressure, there can be no pressure waves, so there is no sound.

But space is is not completely empty and not completely devoid of pressure. Hence, it carries sound. But not in a manner that would match our everyday experience.

For instance, if you were to put a speaker in interstellar space, its membrane may be moving back and forth, but it would be exceedingly rare for it to hit even a single atom or molecule. Hence, it would fail to transfer any noticeable sound energy to the thin interstellar medium. Even the somewhat denser interplanetary medium is too rarefied for sound to transfer efficiently from human scale objects; this is why astronauts cannot yell to each other during spacewalks. And just as it is impossible to transfer normal sound energy to this medium, it will also not transmit it efficiently, since its atoms and molecules are too far apart, and they just don’t bounce into each other that often. Any “normal” sound is attenuated to nothingness.

However, if you were to make your speaker a million times bigger, and let its membrane move a million times more slowly, it would be able to transfer sound energy more efficiently even to that thin medium. And that energy would propagate in the form of (tiny) changes in the (already very tiny) pressure of the interstellar medium, i.e., it would be sound.

So yes, sound can travel in the intergalactic, interstellar, interplanetary medium, and very, very low frequency sound (many octaves below anything you could possibly hear) plays an important role in the formation of structures (galaxies, solar systems). In fact, this is the mechanism through which a contracting cloud of gas can shed its excess kinetic energy and turn into something compact, such as a star.

How fast do such sounds travel, you ask? Why, there is no set speed. The general rule is that for a so-called perfect fluid (a medium that is characterized by its density and pressure, but has no viscosity or stresses) the square of the speed of sound is the ratio of the medium’s pressure to its energy density. The speed of sound, therefore, can be anything between 0 (for a pressureless medium, which does not carry sound) to the speed of light divided by the square root of three (for a very hot, so-called ultrarelativistic gas).

This post originally appeared on Quora. Click here to view.

The Orionid Meteor Shower Peaks This Weekend


October is always a great month for skywatching. If you missed the Draconids, the first meteor shower of the month, don't despair: the Orionids peak this weekend. If you've ever wanted to get into skywatching, this is your chance.

The Orionids is the second of two meteor showers caused by the debris field left by the comet Halley. (The other is the Eta Aquarids, which appear in May.) The showers are named for the constellation Orion, from which they seem to originate.

The shower is expected to peak overnight from Sunday, October 21, to Monday, October 22, when you can plan to see 15 to 20 super-fast meteors per hour. The best time for viewing is between 2 a.m. and 5 a.m., when Orion appears completely above the horizon. Make a late-night picnic of the occasion, because it takes about an hour for your eyes to adjust to the darkness. Bring a blanket and a bottle of wine, lay out and take in the open skies, and let nature do the rest.

There's a chance that the Moon might interfere with the meteors' visibility, according to Space.com. Leading up to its full state on October 24, the Moon will be in a waxing gibbous phase, becoming larger and brighter in the sky as the Orionids speed past Earth. Limiting light pollution where you can—such as by avoiding city lights—will help.

If clouds interfere with your Orionids experience, don't fret. There will be another meteor shower, the Leonids, in November, and the greatest of them all in December: the Geminids.

A version of this story appeared in 2017.