What happens on the surfaces of our closest neighbors? Farther away, are there places like our own, with their own populations wondering at the skies? Hubble has watched stars and planetary systems in the making, examined planets around distant stars, and witnessed the destructive power of cosmic impacts.

The Birth of Stars and Planets

Glowing jets beam forth from the peak of a cloud of gas and dust in Carina Nebula. Infant stars buried within the cloud are creating the jets.

New stars form out of collapsing clouds of gas and dust, as gravity pulls material together into a dense object surrounded by a spinning disk of leftover matter. Eventually, the young star erupts with jets of intense radiation trillions of miles long, traveling at 500,000 miles (800,000 km) per hour. Scientists are still unsure exactly how the jets form, but believe they result from magnetic fields emanating from the forming star.

Before Hubble, astronomers could see the jets, but not the star-forming disks. Hubble’s vision allowed them to see both. In 1995, it took the first detailed images of jets and disks in the Orion Nebula.

Hubble has since taken many images of jets, and found the first direct evidence that they originate at the center of the dusty, gaseous disk the star is drawing on for its raw material. The jets are thought to play a major part in star formation, perhaps slowing down the spinning disk so more matter can collect onto the star.

A cavern of gas and dust in the Orion Nebula contains 700 young stars in various stages of formation.

Astronomers once thought that the disks of dust around stars that coalesce into solar systems, called protoplanetary disks, would be impossible to see. The disks were hidden inside larger clouds of gas and dust, making them difficult to discern.

Scientists take a closer look at star formation in the Orion Nebula - and some of the puzzles involved.

Two of the many embryonic planetary systems in the Orion Nebula. These disks of gas and dust left over from the formation of a new star give rise to solar systems.

Enlarge image for more examples.

Hubble torpedoed this idea, finding numerous protoplanetary disks. Its observations have shown that the environment in which a star develops influences its prospects for planet formation. Hubble observations have also given scientists clues about the missing steps in our knowledge of planet formation – for instance, just how a disk of gas and dust evolves into individual planetary bodies circling the newborn star.

Extrasolar Planets

Hundreds of extrasolar planets have been discovered beyond our solar system. Most have been found by ground-based telescopes looking for tiny wobbles in the motion of a star as a planet tugs at it, or by the slight dimming of light as a planet passes in front of its parent star.

For the latter, Hubble can provide a more in-depth look, watching these light-blocking periods, called “transits,” for clues about the planets that cause them. Thus far, Hubble has made the first measurements of the composition of planets around other stars, finding atmospheres containing sodium, carbon and oxygen, and a planet with a comet-like tail of hydrogen evaporating into space. It also found the first organic molecule on an extrasolar planet: methane in the atmosphere of a Jupiter-sized planet blisteringly close to its star.

A scientist explains the discovery of Fomalhaut b, the first extrasolar planet captured on camera in visible light.

Astronomers blocked light from the star Fomalhaut, in the center of this image, in order to see the much dimmer planet as it passes through the dust ring around the star. Images taken months apart show the planet moving along its expected orbit.

Enlarge Image

Hubble also did what astronomers thought might not be possible: Take the first visible-light picture of a planet. In an image of the dust belt around a star, a tiny speck is planet Fomalhaut b: a world approximately three times the size of Jupiter and possibly surrounded by a bright disk of gas and dust.

Astronomers had suspected since the early 1980s that the star Fomalhaut might have planets, based on observations of its dusty surroundings.

Comet Crashes

First Strike

A fragment of Comet Shoemaker-Levy 9 collides with Jupiter, raising a plume of debris more than 600 miles high as it strikes with the force of 225,000 megatons of TNT. The fragment was one of the smaller pieces to strike the planet.

In 1994, Comet Shoemaker-Levy 9 plunged into the atmosphere of Jupiter, sending great plumes of debris blossoming from the planet. Hubble had a spectacular view of the event, monitoring the comet as it approached the collision. It observed the comet, which had been shattered into dozens of fragments by Jupiter’s gravity, and watched as violent waves rippled away from the impact sites. It was a once-in-a-thousand-years-event – or so scientists thought.

In May 2009, astronauts visited Hubble to install new instruments and make repairs. In July, while engineers and scientists were still in the process of testing and adjusting the refurbished telescope, an amateur astronomer discovered a strange dark spot bruising Jupiter’s surface. The gas giant had been struck again. An asteroid had streaked unnoticed into the planet, leaving an expanding impact site in its wake.

The Hubble team temporarily set aside its schedule to take pictures of the impact site with one of its new instruments. The rare event was too important to miss.

Hubble’s images of Jupiter’s impact sites raise questions about the composition of the planet. For instance, the properties of the waves racing outward from the Shoemaker-Levy 9 sites indicate that the planet’s composition is less similar to that of the Sun than scientists previously believed. One of Hubble’s advantages is its ability to take high-quality images of such events on short notice, providing observations that deepen our understanding of our cosmic neighborhood.

Jupiter Impacts

In July 2009, an asteroid struck Jupiter, leaving a bruise the size of the Pacific Ocean. Hubble engineers interrupted the telescope’s calibration after a recent servicing mission to snap a shot of the impact.

Images taken of Jupiter in visible and ultraviolet light on July 17, 1994, show impact sites in the southern hemisphere. Enlarge for a detailed explanation

The brief interval between the impacts provokes the question of whether these events are as rare as previously thought. Scientists thought impacts in our solar system happen thousands of years apart. The timing of these incidents might be coincidental, or it could mean collisions happen more frequently than we suspect.