Understanding Impacts on Jupiter: No Solid Surface, Dramatic Atmospheric Entry

Question:If Jupiter is a gas planet, how can objects like comets or asteroids cause significant impacts on its surface? Wouldn’t these objects just go through the planet like a plane through a cloud?

Answer:This is a great question! Jupiter, the largest planet in our solar system, is indeed a gas giant primarily composed of hydrogen and helium. Unlike Earth, it lacks a solid surface. However, the fact that Jupiter is a gas giant does not mean that objects like comets or asteroids simply pass through it. Instead, these objects encounter the planet's dense and layered atmosphere, which increases in pressure and temperature as one descends. This creates a dramatic phenomenon that scientists have observed and studied.

Atmospheric Entry

When objects like comets or asteroids enter Jupiter's atmosphere, they experience intense friction and heating. This happens because of the dense gas that surrounds the planet. Due to this friction, the object can break apart or disintegrate before reaching deeper layers of the atmosphere. This process is known as atmospheric entry.

Impact Phenomena

Even if the object does not disintegrate completely, it can still create significant impacts in the upper atmosphere of Jupiter. These impacts result in bright flashes of light and shock waves, which can be observed from space and even from Earth with telescopes.

For example, the 1994 collision of the Comet Shoemaker–Levy 9 with Jupiter was a fascinating event. This comet, which broke apart from tidal forces, fell with a speed of approximately 60 km/s, hitting Jupiter between July 16 and 22, 1994. The fragments ranged up to 2 km in diameter. They did not go through the planet like a cloud; even the largest fragments were destroyed when the pressure reached 250 kPa (36 psi).

No Solid Surface

Since Jupiter lacks a solid surface, the concept of impact differs from what we observe on terrestrial planets. Instead of a physical impact on a surface, the effects are more akin to explosive interactions with the atmosphere. The energy released during such impacts can produce visible effects such as bright fireballs or atmospheric disturbances.

Comet Shoemaker–Levy 9 Impact Details

During the Comet Shoemaker–Levy 9 impact, instruments on the Galileo spaceship detected a fireball that reached a peak temperature of about 24,000 K (23,700 °C, 42,700 °F). This temperature is significantly higher than the typical Jovian cloudtop temperature of about 130 K (143 °C, 226 °F). The fireball expanded and cooled to about 1500 K (1230 °C, 2240 °F) in about 40 seconds. The fireball reached a height of over 3000 km (1900 mi). A few minutes after that, the falling material caused another increase in heat, producing a large dark spot over 6000 km (3700 mi) across, which could be seen by small telescopes on Earth.

Over six days, there were 21 impacts. On July 18, the biggest fragment hit Jupiter with the impact labeled "G," creating a dark spot over 12,000 km (7500 mi) across. Scientists estimated that it released an energy equivalent to 6,000,000 megatons of TNT (600 times the world's nuclear arsenal).

The impacts generated enormous waves that swept across Jupiter at speeds of 450 m/s (1476 ft/s) and were observed for over two hours after the largest impacts.

The Composition of Jupiter

While Jupiter is called a "gas giant," the hydrogen and other elements that on Earth would be gases are under such incredible pressure from the huge gravity caused by the immense size of Jupiter. The hydrogen and helium gas that make up the bulk of Jupiter's atmosphere simply get denser and denser the farther down you go until the hydrogen becomes a liquid metal. The core is either liquid metallic hydrogen or it is solid, then there is liquid hydrogen, and then the atmosphere.

.jpg" alt"The image of Jupiter's atmosphere during the impact of comet Shoemaker-Levy 9" />

The image was taken on 20 July 1994 at near-infrared wavelengths with the infrared camera MAGIC at the 3.5-m telescope at the German-Spanish Calar Alto Observatory. At the lower left rim of the planet, the explosion cloud produced by the impact of one of the last fragments of the comet is visible. The bright spots to its right are the hot traces left by impacts of other fragments.

Refer to the image to see the impact of the comet on Jupiter's atmosphere. This event showcased just how powerful and dramatic impacts can be on Jupiter despite the lack of a solid surface.

For more information on Jupiter and its atmospheric phenomena, visit ESA Science Technology.