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A comparison of the two newly-discovered planets with Venus and Earth. Image courtesy of NASA/Ames/JPL-Caltech

Yesterday, scientists at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts made a major announcement. For the first time, after years of searching, Earth-sized planets had been detected outside of our solar system. Among the five planets in the distant Kepler-20 star system are Kepler-20e and Kepler-20f—two rocky orbs with diameters approximately 87 percent and 103 percent that of earth, respectively. The news has the scientific world in a state of excitement over the consequences of the find. We spoke with Smithsonian astrophysicist Francois Fressin, the lead author of the paper, about the discovery.

The Basics

Researchers have been using the Kepler space telescope since it launched in March of 2009 to search for exoplanets, or planets in other solar systems. “Kepler is staring at 200,000 stars, all located in the same area of the sky, and it just monitors the light it gets from each of the stars, continuously, for years,” says Fressin. “For a fraction of the stars, there’s a periodic dimming with the same duration and same depth of light.” This dimming can be caused by a small opaque body crossing between the star and the telescope—in this case, a pair of planets. The team first detected the telltale dimming more than a year ago, but had to make more calculations with custom-developed software to rule out the possibility that it was caused by other phenomena.

From the degree and frequency of the dimming, the scientists are able to make inferences about the planets. Kepler-20e and Kepler-20f are 6,900 miles and 8,200 miles in diameter, respectively, remarkably close to Earth’s 8,000 mile size. Because the two planets are so close to their host star—they orbit at 4.7 million miles and 10.3 million miles, both far closer in than Mercury is to the sun—they are believed to be extremely hot, with average temperatures of 1400 and 800 degrees Fahrenheit, respectively. “We know they’re both pure rock bodies,” Fressin says. “But we don’t have precise mass estimates, so we can’t say if they’re similar in composition to the Earth, or something denser with more iron, like Mercury.”

An artist's conception of Kepler-20e. Image courtesy of NASA/Ames/JPL-Caltech

What It Means For Astronomy

Exoplanet hunters began uncovering distant gas giants as early as 1992, but smaller, Earth-sized bodies had proved more difficult to detect. “We’ve crossed the threshold: this the first time that humanity is able to detect an Earth-sized object around another star,” Fressin says. ”That’s symbolically and technologically important.”

The discovery represents a historic milestone in astronomy. Now, scientists are convinced that they have the right tools to be able to detect Earth-sized planets that might support life. Researchers will continue using the Kepler space telescope to locate exoplanets in hope of finding such a world.

What It Means For Planetary Science

The discovery also turns upside-down much of what scientists believed about the formation of solar systems. The two Earth-size planets are interspersed with three gas giants, all extremely close to the host star, Kepler-20. “From the star, it goes in the order big, small, big, small, big, which seems completely weird,” says Fressin. “In our solar system, we have these four rocky small bodies, and then, farther away, these four large giant gaseous planets. So how did that happen, that we have all this mixing in the Kepler-20 system?”

Although we don’t currently have definitive answers, scientists suspect that the planets drifted into their current position over time. “They didn’t form at the place they are right now, there was not enough rocky material to build these five planets so close to their host star,” Fressin says. “So one solution would be that they formed farther out, and then migrated in.”

What It Means For Extraterrestrial Life

An artist's conception of Kepler-20f. Image courtesy of NASA/Ames/JPL-Caltech

The most tantalizing possibility of these discoveries is the potential that the exoplanets might harbor life. But both Kepler-20e and Kepler-20f are outside the habitable zone—often called the “Goldilocks” zone—that is neither too close nor too far from the host star, allowing for the evolution of living creatures. ”We don’t know a lot of things about life, but we know that one of the main ingredients of life on Earth is the presence of liquid water,” says Fressin. “Right now, at the temperatures estimated, water can’t be in a liquid state on either planet.”

Still, the hypothesis that the planets may have formed farther away, and then migrated to their current locations close to the star, means that life may have existed long ago. “It seems pretty clear that Kepler-20f once crossed the habitable zone of its host star, after its formation,” Fressin says. “It is the closest object in terms of size to the Earth in the known universe, and this means that it could have been habitable in its past.”

What It Means For Space Exploration

Although Kepler-20 is much too far to attempt as the target of a space probe mission—it’s about 950 light-years from Earth, which would require a journey of 36 million years by the space shuttle—Fressin feels that discoveries like this should stimulate interest in the very real possibility of exploring other, closer, star systems. “It would be challenging, and would require great international collaboration, maybe for one or two generations, but it would be feasible,” he says.

Such a mission would admittedly be very long-term, but the rewards are many. “I think the best location to send a probe would be to the closest sun-like star,” says Fressin. “So then imagine, in two generations, we’d have the probe coming back with pictures—real pictures—of another world.”

The cover and record "The Sounds of Earth," included aboard the Voyager 1 and 2 probes. Photos courtesy of the Air and Space Museum.

If, billions of years from now, extraterrestrials were to come across one of our far-flung interstellar space probes, what could they learn of us? In the 1970s, as NASA prepared to send its first probes beyond the distant reaches of the solar system, this was the question that worried renowned scientist and author Carl Sagan.

Sagan, who died 15 years ago on this day, was enormously influential in a number of ways—he was a prolific researcher and publisher of articles on planetary science, and his books and popular PBS series Cosmos inspired a generation with the remarkable discoveries of astronomy and astrophysics. But his most long-lasting and significant impact might indeed be the time capsule he placed on the NASA probes: a gold-plated record titled “The Sounds of Earth.”

“From the beginning, Sagan was a strong believer in the probability that there is intelligent life out there,” says Jim Zimbelman, a geologist at the Air and Space Museum, which holds a replica of the gold record in its collection. “And because of that, he said, ‘Look, these are the first man-made objects to leave the solar system. What if someone finds them?’”

Sagan was instrumental in having small metal plaques attached to Pioneers 10 and 11, the first probes to leave the solar system, that would theoretically indicate to extraterrestrials the origin of the probe if ever discovered. But for Voyagers 1 and 2—a pair of spacecraft designed to survey Jupiter, Saturn, Uranus and Neptune—he and others wanted something more comprehensive: a record of images and sounds that would represent the diversity of the human experience.

Sagan initiated the decision to put a time capsule of humanity aboard the Voyager space probes. Photo courtesy of NASA.

“How do you do that—how do you capture the world in the a few pictures? That was the challenge,” says Zimbelman. ”On the selection panel, they included historians, artists and people specializing in literature. They just wanted to get a smattering of human culture preserved on the record.” Sagan chaired the committee and presided over the selection process.

Ultimately, 116 images and sounds made it through the selection process and were included on “The Sounds of Earth.” “There are hundreds of digitized images on there, of everything from tribal peoples in Africa to a modern city,” Zimbelman says. Greetings were recorded in 55 different languages, and accompanied by a diverse musical selection with everything from Bach to traditional Peruvian music to Chuck Berry.

Perhaps even more difficult than selecting content for the record was devising a way to help distant, unimaginable life forms figure out how to play it. “The scientists all agreed that they needed to use some timing feature that was not only here on earth, or even in the solar system,” Zimbelman says.

The panel decided to base the speed at which the record should be rotated upon a characteristic of the hydrogen atom. “The atom can be in two different states, and when it transitions from one to the other, it happens in a characteristic time period—its a very small fraction of a billionth of a second,” Zimbelman says. Inscribed upon the metal cover of the record is a series of diagrams that attempt to communicate playing instructions based on this timing. Although critics have argued that extraterrestrials would find these pictures utterly mystifying, they represent the best attempts by scientists to convey information without using any language or conventions of human culture.

At the Air and Space Museum, a full-scale replica of the two Voyager spacecrafts is on view in the Exploring the Planets gallery, and an interactive display allows visitors to see some of the images and hear some of the sounds included on the golden record. Parts of the replica were used in pre-engineering tests before the probes were launched.

Meanwhile, more than 34 years after their 1977 launches, the Voyagers are still in the early stages of their journeys, hurtling through limitless space with the gold records safely aboard. After flying by the outer planets of the solar system, they are now traveling beyond its outer reaches—Voyager 1 is 120 times further from the sun than Earth is, and Voyager 2 is about 98 times further.

Given enough time, they just might reach other star systems and perhaps even other planets. And if extraterrestrial life forms happen upon them, thanks to Sagan, they just might be able to learn a little bit about life on earth. But, Zimbelman cautions, we need not hold our breath—nothing is happening anytime soon. ”Voyager 1 will get within a light year of a star about 400,000 40,000 years from now,” says Zimbelman. “It’s very, very long-term.”

A model of Conrad F. Bartling's 1888 fence-building machine. Photo courtesy of the American Art Museum.

Need to make a paper bag in a hurry? Having trouble getting your pigeons to startle? Is your buggy rattling too loudly? These are some of the questions that inspired inventors in the mid-19th century. When they tried to patent their imaginative devices, they were required by law to include small-scale models to the Patent Office.

“Inventing a Better Mousetrap: Patent Models from the Rothschild Collection,” a new exhibition at the American Art Museum, features an array of these intricate mechanical invention models, including the aforementioned paper bag making machine, pigeon starter, and, of course, the “better mousetrap” itself. “The creation of these models was really a mini-industry,” says Charles Robertson, deputy director emeritus of the museum, and curator of the exhibition. ”And as you can see, some of these are masterpieces of craftsmanship.”

This isn’t the first time these models have seen this space. The museum is housed in one of the country’s finest examples of Greek Revival architecture. Construction on the building (which is also home to the National Portrait Gallery) began in 1836 and was completed in 1868 . But it was originally created for a much different function.

“Most people that visit don’t know the building was originally the Patent Office Building,” says Robertson. “Since it was built for this purpose, we thought it was really appropriate to have some historic connection.”

True to its reputation as “a temple to the industrial arts,” the Patent Office Building displayed more than 200,000 models in its lifetime, including the 32 selected for this exhibit. “The law required that a patent model be submitted with every patent application,” says Robertson. “Twenty-five to thirty-five thousand patent applications were being submitted a year, each of which required a model, and some of them were really masterpieces of craftsmanship.” Soon, an entire model-making industry sprang up around the Patent Office Building to craft delicate working miniatures of each invention.

The models exemplify the remarkable—and occasionally harebrained—degree of innovation that defined the era. “Compared with England and France, we had two, three, and even four times as many patents as those two countries put together,” says Robertson. “There was really a ferment of invention.”

Standing in this building, surrounded by tiny, bizarre contraptions, it’s easy to feel transported back to the heyday of the industrial era. The variety of inventions ranged from the simple—a sliding extension ladder similar to ones used today—to the elaborate—the theft prevention device, which rigged a weighted chain to set off a loaded pistol if intruders tried to open the door. Many were made possible by the speed of technological advances. The 1877 electro magnetic railroad signal would have been unimaginable when George Washington signed the soap-making patent on display just a few yards away.

Some of the devices—most of which never made it to commercial production—are downright perplexing. “It’s difficult, sometimes, to really figure out what they even were, because these things were invented 100 to 150 years ago,” Robertson says. The exhibit even features a “Mystery Model” section, where visitors can try to guess what each model is supposed to do.

A model of H. Hallock's 1858 life-preserving stateroom. Photo courtesy of the American Art Museum.

The life preserving container is one of several items that might confuse the untrained eye. “It’s this metal thing that looks like it has two eyes,” says Robertson. “It really seems like something out of a Jules Verne novel, or even a spaceship.” The invention was intended to be attached to the side of a ship and discharged in case of emergency, and was outfitted with sleeping quarters, storage for provisions, and a sliding hatch for light and air.

Submission of models with applications was eventually banned in 1880. These 32 models have traveled a long, rocky path back to the Patent Office Building; first, a fire destroyed 87,000 models in 1877, and by 1924 the Patent Office decided to dispose of the survivors. Most were purchased by Sir Henry Wellcome, who intended to create a model museum before the 1929 stock market crash thwarted his plans. Another fire destroyed 15,000 of his collection.

Eventually, in 1997, they found their way to Alan Rothschild, a collector who holds more than 4,000 models—the largest private collection of American patent models in existence.  Now that they’ve returned to the Patent Office Building, it’s clear that even in today’s hi-tech world, the models retain the power to capture our imaginations.

Inventing a Better Mousetrap: Patent Models from the Rothschild Collection is on display at the American Art Museum until November 3, 2013. View the full slideshow of the items on display online.

With additional reporting from Aviva Shen.

Join curators to learn about "Pair of Prickly Pairs" as part of a gallery talk. Photo courtesy of the Renwick Gallery

Monday, December 19 Fly Me To Mars

Author and illustrator Catherine Weitz’ award-winning children’s book Fly Me To Mars tells the story of wayward planet on a fantasy journey. Weitz, a senior scientist at the Planetary Science Institute, focuses on Mars geology in her research. Come meet Dr. Weitz and have your copy of the book signed in time for the holidays. Free. 11 a.m. to 2 p.m. Air and Space Museum, at the entrance to the museum store.

Tuesday, December 20 Holiday Arts and Crafts

Join museum staff for a morning of arts and craft making with a holiday theme. Participants will have their own chance to create memorable ornaments with materials provided by the museum. Free; please call 202 633 4844 to make reservations. 10:30 a.m. to 12:30 p.m. Anacostia Community Museum, program room.

Wednesday, December 21 American Craft Masterpieces

As part of the Renwick’s monthly gallery talks series, experts discuss the masterpieces in small, intimate groups. This month, join Rebecca Robinson as she provides insight into Jon Eric Riis’ Pair of Prickly Pairs. Riis is an internationally-known tapestry artist whose intricate works often incorporate precious materials such as metallic and silk threads. Pair of Prickly Pairs was acquired by the museum in 2001 and features an unusual cactus-like roughness on the surface of the fruits that was produced with the incorporation of glass seed beads into the work. Free. 12 p.m. Renwick Gallery, first floor lobby.

Thursday, December 22 Butterfly Pavilion

Come out of the chill of winter and discover a tropical oasis in the middle of the Mall. Located next to the “Butterflies + Plants: Partners in Evolution” exhibit at the Natural History Museum, the Butterfly Pavilion is home to hundreds of rare butterflies and exotic plants from all over the world. Tickets are required, and can be purchased in person at the Butterfly Pavilion Box Office or online. $6 for adults, $5.50 for seniors (60+), $5 for children (2 to 12), and $5 for members. Natural History Museum, 2nd Floor West, open 10:15 a.m. to 5:00 p.m. daily.

For a complete listing of Smithsonian events and exhibitions visit the goSmithsonian Visitors Guide. Additional reporting by Michelle Strange.

World War I soldiers writing letters home. Photo courtesy of the National Postal Museum

With the war in Iraq officially declared over yesterday, it seemed appropriate to head to the National Postal Museum to reflect upon the experiences of servicemen who are stationed abroad. “Mail Call: A History of America’s Military Mail,” an exhibition that opened last month, tells the stories of individual soldiers through their mail, and traces the history of mail delivery for the military from the Revolutionary War through today.

“Mail sustains the spirits, both on the home front and for the people who are on the front line,” says Lynn Heidelbaugh, curator at the museum. “We wanted to show visitors how it keeps up this connection, and keeps up this sense of community.”

The exhibition features a number of letters that serve as windows on the personal lives on soldiers stationed abroad. One was sent by John H. Zimmer, a serviceman stationed in France during World War I, to his younger sister Frances. “Just a few lines to let you know that I received your letter today and was very glad to hear from you,” he wrote. “I haven’t been getting many letters for several weeks until today when I received seven. But gee, I was awful glad to get them.”

The show also covers the evolution of the military mail system across the full sweep of its history, starting with the country’s founding. “Mail was really expensive during the Revolutionary War—most people were writing just for business purposes, because postage was too much to use otherwise,” says Heidelbaugh. Over time, as prices came down, mail became the sole source of communication between distant points. With the Spanish-American War and World War I—the first U.S. global wars—the challenges confronting the Postal Service grew dramatically.

A letter from Operation Desert Storm. Photo courtesy of the National Postal Museum.

Mail officials responded with a number of innovations, sending postal employees around the world to carry out the mission. During World War II, the Postal Service promoted the sending of “Victory Mail,” which were letters written on a standardized stationary and projected onto microfilm to save shipping weight. The reels of microfilm were sent to processing centers abroad, and letters were reproduced on quarter size pieces of paper to be delivered to recipients.

Audio reels were sometimes used during the Vietnam War for the same reason. ”We have one recording from a soldier stationed in Vietnam,” Heidelbaugh says. “He actually talks about what mail has meant to him, and his outlook in the future—everything you expect in a letter from wartime.”

When all of the varied locations where mail is delivered during times of war is considered, the strategic operation is mind-boggling. “The Postal Service tries to make sure that all services are available to everyone,” Heidelbaugh says, “whether they’re in a tent somewhere or in a submarine.” On display is an actual door from the post office that was aboard the U.S.S. Thomas S. Gates, a Navy cruiser, as well as a camouflaged, waterproof mail bag that was used for aerial mail drops to troops in the jungles of Vietnam.

Other items in the exhibition remind visitors of the grim truth of war. Many letters bring news of horrific tragedy. One is a Certified Mail stamp that was salvaged from the Naval base at Pearl Harbor, Hawaii. The date on the stamp is still December 6, 1941—the day before the infamous attacks on the base that claimed the lives of thousands.

The other is a letter addressed to a Union soldier’s wife at the height of the Civil War. “One of the pieces I find most touching—and sadly, the most typical kind of letter—is this condolence letter,” says Heidelbaugh. “It’s from a commanding officer, and he’s had to write to a widow, and confirm that her husband has died in a POW camp.”

Appropriately, the show concludes with a package sent from the recent conflict in Iraq. ”We chose this because it’s representative of contemporary mail,” says Heidelbaugh. The package was sent by Chief Warrant Officer Peter Paone to his son Tom, back in Pennsylvania, and carried souvenirs from his time abroad. “A lot of people ask, ‘with so many more options for communication now, what are people even sending mail for?’ But there’s no other way to send packages. We wanted to show people that mail is still vitally important.”

“Mail Call: A History of America’s Military Mail” is on display at the National Postal Museum