Planetary Sciences Feature

Ten New Frontiers in the Solar System and Beyond

Humanity’s reach has extended from the surface of Earth to the very edge of our solar system, even to exoplanets far into space. What’s next in our journey into the unknown?

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Space: the final frontier.

Even if you’re not a Star Trek superfan, those words still ignite a yearning for knowledge. We’ve explored across land, across oceans, and deep into those oceans; inevitably, we’ve turned our ambitions skyward. In the mid-20th century, we sent humans into orbit, onto the Moon. And with a still-simmering urge to learn, we’ve found ways to remotely explore our Sun and the planets and moons of our solar system, with plans brimming to one day send humans into interplanetary space.

In 1999, the United Nations held the first World Space Week, which this year features more than 2,000 events across the world. The week started Wednesday, 4 October 2017, on the 60th anniversary of Sputnik’s launch.

With a theme of “Exploring New Worlds in Space,” World Space Week inspired us at Eos to look back on our past coverage of all things space and look ahead to what’s in store for future explorers. Here are 10 ways space exploration opened our eyes to our celestial neighborhood and beyond, along with the ways we plan to boldly go where no human—or spacecraft—has gone before.

1. Voyager’s Path to the Edge of Our Solar System

In many ways, the Voyager program epitomizes humanity’s quest to journey into the beyond.

“As the first spacecraft to fly by all four giant planets in the outer solar system, Voyager produced a bonanza of new science,” wrote Jim Green, director of NASA’s Planetary Sciences Division, in a NASA article honoring Voyager’s legacy. “Voyager paved the way for a number of NASA missions,” including Cassini, Galileo, Juno, New Horizons, and the Europa Clipper, the latter a project currently under development.

Launched 16 days apart in 1977, Voyager 1 and 2 each visited Jupiter and Saturn, providing the first glimpses of Io’s volcanic activity and hinting at the complexities within Saturn’s rings.

Voyager 1 then traveled on a direct line out of the solar system. Before becoming the first spacecraft to cross into the heliopause, Voyager 1 turned its eyes back toward home one last time and in 1990 gave us the “Solar System Family Portrait,” a sequence of images that shows Venus, Earth, Jupiter, Saturn, Uranus, and Neptune all in their places around the Sun. Seeing Earth as a “Pale Blue Dot,” as famed cosmologist and science communicator Carl Sagan called it, emphasizes our planet’s sheer diminutiveness and delicacy as it hangs in the vastness of space.

World Space Week: Voyager 2 view of Neptune
Voyager 2 snapped this shot of Neptune’s Great Dark Spot surrounded by white, high-altitude clouds during its flyby of the Neptunian system in the summer of 1989. Credit: NASA/JPL-Caltech

Voyager 2 went on to visit Uranus, observing its moons, faint rings, and strange weather, and then swung past Neptune on its way to interstellar space. It remains the only spacecraft to have visited those two planets.

Now, roughly a month past the 40th anniversary of their launch dates, both Voyager craft continue to transmit data back to Earth as part of the Voyager Interstellar Mission (VIM). The twin space probes are quite literally pushing the boundaries of human exploration as they continue their journeys through the edge of the Sun’s influence.

And the spacecraft will keep pushing outward, past stars. As noted on the VIM website, “The Voyagers are destined—perhaps eternally—to wander the Milky Way.”

2. Next Stop: Mars

In 1965, Mariner 4 beamed the first images of the Martian surface to Earth, and humans have been captivated by the Red Planet ever since. In addition to orbiting scientific platforms like the Mars Atmosphere and Volatile Evolution mission (MAVEN) and the Trace Gas Orbiter, Mars currently hosts 14 human-built robots, but only 2—the Mars Science Laboratory (Curiosity) and the Opportunity rover—are still in operation.

World Space Week: Curiosity rover selfie
NASA’s Curiosity rover taking a selfie using its Hand Lens Imager camera on 5 August 2015. Credit: NASA/JPL-Caltech/MSSS

More robots are getting ready to explore our rocky neighbor and look for signs of current or past life, like biological signatures or water. Soon to join the fleet is Mars 2020, a rover that will be able to collect a high volume of samples and cache them on the planet’s surface for future return to Earth. The rover “will explore one of several possible paleoenvironments older than 3.5 billion years that might once have been conducive to microbial life,” project scientists wrote in Eos earlier this year.

There’s also the Mars Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander, which NASA plans to launch in May 2018. Mars InSight will be equipped with a seismometer to listen for “Mars-quakes” rumbling beneath the planet’s subsurface.

3. Life in the Gas Giants’ Moons?

When Cassini flew through Enceladus’s plumes in 2005 and detected water shooting out of the icy surface, a paradigm changed. No longer did the potential for life exist on just Mars and the other rocky inner planets. Suddenly, the outer solar system opened wide for possible signs of life.

World Space Week: Cassini view of Enceladus
Cassini captured this image of Enceladus, with its south pole plumes of water shooting into space, from a distance of 777,000 kilometers. Credit: NASA/JPL-Caltech/Space Science Institute

Further discoveries of molecules in Enceladus’s plumes revealed that “Enceladus satisfies almost all of the present criteria that define habitability,” said Hunter Waite, principal investigator on Cassini’s Ion and Neutral Mass Spectrometer. The spacecraft also found prebiotic chemistry in Titan’s atmosphere.

Back here on Earth, scientists are developing new tools to explore these icy worlds, should we ever get there. Engineers at NASA are working on the Europa Clipper orbiter, set to launch sometime in the 2020s.

In addition, a team working in Greenland recently tested a new instrument to study the molecules in the walls of ice boreholes. Such an instrument could be affixed to a future Europa lander (although, for now, this lander remains a hypothetical mission that scientists are currently conceptualizing as a thought experiment).

4. Juno’s Current Dance With Jupiter

Now that Cassini has ended, eyes are turning to Saturn’s neighbor, Jupiter. NASA’s Juno satellite began orbiting the planet on 4 July 2016, its primary mission being to understand the origin and evolution of Jupiter and its moons. This mission includes mapping Jupiter’s complex magnetic field, pinning down the water content of the planet, and studying its storms and auroras in unprecedented detail.

World Space Week: Juno view of Jupiter storm
Juno captured this image of a storm in motion near Jupiter’s north pole, called the “North North Temperate Little Red Spot 1,” during the craft’s seventh close flyby of the planet. Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Seán Doran

So far, scientists have seen densely packed clusters of Earth-sized storms that somehow coexist, a stronger and lumpier magnetic field than expected, and auroras that don’t behave according to physics seen on Earth. “There is so much going on here that we didn’t expect,” Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio, told Eos. “We have had to take a step back and begin to rethink of this as a whole new Jupiter.”

One unique feature of the Juno mission is JunoCam, a visible light imager whose goal is to image Jupiter’s polar regions … and anything else on Jupiter the public deems interesting. That’s right: the public.

During each of its 12 scheduled close flybys, JunoCam will image sections of the planet’s atmosphere that you and others have nominated, discussed, and voted as the most interesting. This is the first time NASA has opened up an active mission to real-time participation from the public.

“We’re all in, in the sense that I don’t have a team of scientists and image processors waiting in the wings in case the public doesn’t show up,” Candy Hansen, senior scientist at the Planetary Science Institute and lead scientist on the JunoCam instrument, told CBS News. “We are entirely, 100 percent, relying on the public. And some of them have done fabulous work.”

NASA releases JunoCam images in their raw form, which has led to some rather spectacular and creative interpretations by the public, like this fractal representation of the Great Red Spot:

5. A Window to Pluto

Although it’s been 11 years since Pluto was recharacterized as a dwarf planet, excitement about the world never waned. Enter the New Horizons probe, launched in 2006, which took pictures of Pluto as it whizzed by in July 2015. New Horizons showed that the name “dwarf planet” doesn’t minimize the significance of our tiny, faraway neighbor.

World Space Week: Tenzing Montes on Pluto
NASA’s New Horizons spacecraft captured this image of Pluto’s Tenzing Montes mountain range, located at the bottom right side of its famous “heart,” on 14 July 2015 during its flyby of the dwarf planet. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/SwRI

New Horizons’ images baffled the scientific community. The spacecraft revealed a possibly geologically active surface, covered by flowing glaciers and scoured by strange crevices underneath a blue haze and possibly even clouds.

No one expected such a complex world. “Even I underestimated what we would find,” said Alan Stern, principal investigator of the New Horizons mission.

Currently, New Horizons is sailing toward another object in the Kuiper Belt called 2014 MU69, a reddish, rubber-duck-shaped object orbiting 6.5 billion kilometers from the Sun. Scientists think that 2014 MU69 is a relic of the infant solar system that has remained in the same orbit for the last 4.5 billion years—which means it might be able to tell scientists about the beginning of the solar system. The New Horizons probe will reach 2014 MU69 on 1 January 2019.

6. Peering into the Solar System’s Past with Asteroids and Comets

Four years before New Horizons visited Pluto, NASA’s Dawn spacecraft was exploring our second largest asteroid, Vesta. Dawn orbited Vesta from July 2011 through early September 2012 and sent back detailed geographical maps, topological measurements, and the distribution of minerals on Vesta’s surface.

Dawn left Vesta in 2012 and sailed to the largest object in the asteroid belt, the dwarf planet Ceres. Since its arrival in March 2015, we have seen a probable cryovolcano and deposits of salty material that hint at recent geologic activity. There may even be underground deposits of liquid water. Dawn is still alive orbiting Ceres, having just celebrated the 10th anniversary of its launch on 27 September.

World Space Week: Dawn image of Ceres
Dawn took this series of images of Ceres from an altitude of 20,000 kilometers as the craft orbited exactly between the dwarf planet and the Sun. Ceres’s “bright spot” in Occator Crater can be seen moving from left to right. The brightness is thought to be a recent deposit of salty ice. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

In 2014, the European Space Agency’s Rosetta spacecraft became the first craft to orbit one of the solar system’s “dirty snowballs,” comet 67P/Churyumov-Gerasimenko (67P/C-G). It became the first to land a probe on a comet shortly thereafter, the short-lived Philae.

While in orbit, Rosetta characterized the comet’s gravity, distribution of mass, surface composition, and odd features like cracks and bumps. On 30 September 2016, Rosetta crashed—on purpose—into the comet’s surface, collecting and transmitting data through its final seconds.

Astronomers will soon visit another relic from the solar system’s birth, the carbon-rich asteroid Bennu. On 8 September 2016, NASA launched the Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx), which will approach and study Bennu, retrieve a sample from its surface, and then return the sample to Earth.

Bennu, like Vesta, Ceres, and 67P/C-G, should provide a firsthand account of the conditions in the solar system 4.5 billion years ago. OSIRIS-REx completed a successful slingshot past Earth on 22 September and is now on course for its August 2018 rendezvous with Bennu.

7. Exploring the Cosmos with Powerful Telescopes

With telescopes, spectrometers, and interferometers spread across Earth’s surface to 1.5 million kilometers away in space, humans are peering across and past the solar system.

World Space Week: Pillars of Creation
The so-called Pillars of Creation, a giant star-making factory in the Eagle Nebula, some 7,000 lightyears away. Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA)/J. Hester, P. Scowen (Arizona State U.)

The Hubble Space Telescope, launched in April 1990 and orbiting Earth about 550 kilometers away, gave humanity its first glimpse of the multitude of galaxies beyond us in its Deep Field images. It showed us the towering columns of gas that incubate infant stars. Hubble also gave us glimpses into the auroras of the outer planets and even the atmospheres of exoplanets orbiting other stars.

Then there’s Kepler space telescope orbiting 1.5 million kilometers away, which blasted wide open our view of other worlds beyond our Sun. Since 2009, the Kepler telescope has spotted nearly 4,500 exoplanets—some are Earth sized, whereas others are several times larger than Jupiter.

Joining the exoplanet hunt is the Spitzer Space Telescope, which scans deep space with infrared light. The European Space Agency launched their telescope Gaia in December 2013, with a goal to create a precise 3-D map of the galaxy by imagining 1% of the galaxy’s 100 billion stars. From Earth, the Laser Interferometer Gravitational-wave Observatory (LIGO) measured the waves of shaking space-time from the collision of two black holes.

8. Finding Bizarre Extrasolar Planet Systems

On 22 February, scientists with the Spitzer telescope announced the discovery of a relatively nearby solar system that contained not one, not two, but seven Earth-sized planets in very fast orbits. The planetary system, TRAPPIST-1, came as a surprise to many exoplanet scientists, who had not expected that seven potentially rocky planets could form and coexist around a star like TRAPPIST-1, a dwarf a mere tenth the size of the Sun and about half as hot.

World Space Week: TRAPPIST exoplanets
Artist’s conception of the seven-planet TRAPPIST-1 system, a nearby system of exoplanets that contains the most Earth-sized planets and the most habitable zone planets found in any one system. Credit: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC)

Although all seven of the planets have orbits that would fit well inside that of Mercury’s around our Sun, the host star’s cool temperature allows the outer four planets of the TRAPPIST-1 system to potentially host liquid water. According to Julien de Wit, a planetary scientist at the Massachusetts Institute of Technology in Cambridge, the TRAPPIST-1 planets “are the best targets so far to search for signs of life” outside our solar system.

The TRAPPIST-1 system is but one of many recent exoplanet discoveries that have pushed the limits of plausibility set by scientific theory. KELT-9b, whose 4,300℃ temperature makes it the hottest known exoplanet, circles the hottest known planet-hosting star in a polar orbit instead of a conventional equatorial orbit. The distant gas giant planet HD 131399Ab exists by balancing on the knife’s edge of gravity in a triple-star system, defying the odds by surviving on such a precarious orbit.

And even our nearest stellar neighbor, Proxima Centauri, plays host to a habitable zone terrestrial world, suggesting to astronomers that Earth-sized planets may be ubiquitous in the universe.

9. New Frontiers in Space Science Education

Ensuring the future of space sciences means cultivating a new generation of explorers. In Africa, for instance, a group of researchers and organizations is spearheading the Africa Initiative for Planetary and Space Sciences, a campaign that aims to overcome the continent’s lack of dedicated, well-funded programs. The group hopes that “the fascination for space studies may contribute to driving the younger generation toward higher education in STEM [science, technology, engineering, and mathematics] disciplines.”

High-altitude balloons and CubeSats have opened up the realm of space exploration to students around the world. For example, in California, a group of students (led by a local dad) has been using space-bound balloons to peruse the stratosphere. The high school students of Earth to Sky Calculus affix instruments to their balloons to study the temperatures, pressures, and radiation in the stratosphere. This year, members of the group spread from one end of the United States to the other to see how cosmic rays affected Earth’s magnetic field.

On 21 August, universities, observatories, and scientific organizations across the United States held science events for families to raise excitement for the day’s solar eclipse. Students and citizen scientists launched weather balloons, recorded animal and plant reactions, and peered through telescopes to witness and learn about the celestial event.

10. Creative Ideas to Get Humans into Space

As we learn more about space science, we also push the boundaries of science policy so that we continue to learn more.

NASA administrators, scientists, and former astronauts are calling for the return of humans to the Moon and, beyond that, to Mars. In preparation, the U.S. Senate has pushed for better ways to predict and mitigate the impacts of space weather on humans and technology.

On the international stage, the United States and Russia plan to partner up in creating the Deep Space Gateway, a lunar orbiting station that will serve as a stepping-stone toward a permanent lunar base and a test bed for the technology needed to put humans on Mars. The European Space Agency has begun to consider how to utilize lunar resources to create a sustainable human presence on the Moon.

Independently funded programs also have the goal of getting ordinary citizens into space. Space X aims to offer commercially available space travel and to promote humans living on Mars. And for some, Mars is just the beginning. Breakthrough Initiatives, particularly Breakthrough Starshot, is pursuing interstellar travel to Alpha Centauri.

Incredible Discoveries Ahead

As Carl Sagan once said, “Those worlds in space are as countless as all the grains of sand on all the beaches of the Earth.” The more we study these worlds in our solar system and beyond, the more space continues to tickle humanity’s imagination.

This need to explore unites us, and together, humanity is working steadily to push deep into space’s new frontiers.

—JoAnna Wendel (@JoAnnaScience), Staff Writer; and Kimberly M. S. Cartier (@AstroKimCartier), News Writing and Production Intern

Citation: Wendel, J., and K. M. S. Cartier (2017), Ten new frontiers in the solar system and beyond, Eos, 98, Published on 06 October 2017.
© 2017. The authors. CC BY-NC-ND 3.0