Will Voyager 1 and Voyager 2 be damaged when they pass through the Oort Cloud?

Voyager 1, shown in this illustration, has operated for decades thanks to a radioisotope power system. Credit: NASA via AP

Key Takeaways:

• Voyager 1 and 2, launched in 1977, have traversed the heliopause and are currently in interstellar space, with Voyager 1 significantly farther from the Sun due to its higher velocity.
• The Oort Cloud, a theorized spherical shell of icy bodies surrounding the solar system at a distance of approximately 10,000-100,000 AU, is yet to be directly observed.
• The Oort Cloud is estimated to contain roughly 100 billion comet-sized objects, with a total mass comparable to Earth's, distributed over an immense volume.
• The probability of either Voyager spacecraft colliding with a comet in the Oort Cloud is exceedingly low, likened to winning a lottery jackpot, given the vast distances and sparse distribution of cometary bodies.

Key takeaways sponsored by The Space Store

Will the Voyager 1 and Voyager 2 spacecraft be damaged when they finally pass through the Oort Cloud?

Terry Wilson
North Prince George, Virginia

The Voyager 1 and Voyager 2 spacecraft were launched in 1977. Both passed Jupiter in 1979 and went on to Saturn a few years later, after which Voyager 2 also continued on to Uranus and Neptune. Eventually both entered interstellar space, leaving the heliopause — where the Sun’s solar wind and the interstellar wind of the Milky Way Galaxy meet and are in balance — in August 2012 and November 2018, respectively. As of this writing, Voyager 1 is farther from Earth at nearly 168 astronomical units (AU) from the Sun because it is moving faster (11 miles [18 km] per second, or 3.6 AU per year) than its sister ship (which is moving at 10 miles [16 km] per second, or 3.3 AU per year). One AU is defined as the mean separation between Earth and the Sun, or 93 million miles (150 million kilometers). For reference, Earth’s orbital speed around the Sun is about 6.3 AU per year (19 miles [30 km] per second). 

In 1950, Leiden University astronomer Jan Hendrik Oort theorized the existence of a cloud of comets beyond some 10,000 AU from the Sun, possibly filling the volume dominated by the Sun’s gravitational influence in the Milky Way Galaxy. This volume is an almost spherical bubble stretching as far as 100,000 AU. In comparison, the distance of the nearest star, Proxima Centauri, is about 270,000 AU (4.24 light-years).

So far, the Oort Cloud has not been observed directly, but many visiting comets originate from this enigmatic region. Oort estimated that the cloud would contain some 100 billion comet-sized objects (meaning a radius of 6.2 miles [10 km]). The total mass would be roughly comparable to Earth’s. Some comets, such as Hale-Bopp, are much larger and more massive, but smaller comets are most common.

With a 6.2-mile (10 km) radius, a comet has a surface area of about 116 square miles (300 square km). If we spread out all 100 billion comets, they would cover a surface area roughly comparable to the Sun’s surface. Now imagine that each of these comets is lifted from the Sun’s surface to a distance of 10,000 AU, the inner edge of the Oort Cloud. Each comet will then become separated from its neighbors and the surface area covered by them drops by a factor of about 1/10¹³.

If this is difficult to imagine, here’s a more earthly example: Compare the comets in the Oort Cloud to the 96 million black styrofoam balls dumped in 2015 in the Los Angeles reservoir to prevent evaporation. If we spread those styrofoam balls over the entire Earth’s surface, the probability of finding one of them in your garden is comparable to winning the jackpot in a lottery. These odds are still 100,000 times larger than the probability of Voyager hitting a comet. 

Simon Portegies Zwart
Professor of Computational Astrophysics, Leiden University, Netherlands