Onyx River
The Onyx River is a seasonal meltwater stream in Antarctica’s McMurdo Dry Valleys, regarded as the continent’s longest river.
Also known as: Onyx River Antarctica
How big is it?
32 km · approximate main-channel length
Also 19.88 mi
Approximate main-channel length · approximate
Typical recorded range: 28 km to 35 km.
A little perspective
Onyx River vs Phobos: length comparison
The main-channel length of the Onyx River is about 1.42 times the mean diameter of Phobos.
The Onyx River is a seasonal meltwater stream in Antarctica’s McMurdo Dry Valleys, regarded as the continent’s longest river.
Phobos is the larger and innermost moon of Mars, notable for its irregular shape and heavily cratered surface.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
Onyx River
Approximate main-channel length: 32 km; approximate; range 28 km–35 km.
Antarctica’s seasonal Onyx River is commonly described as approximately 32 km long. Its meltwater course, active reach and mapped endpoints vary with season and survey convention.
US Antarctic Program — Onyx River
The marked approximate main-channel length is calibrated. Unmeasured illustration details are representative.
Phobos
Representative mean diameter: 22.53 km; approximate; range 18 km–27 km.
Mars’s larger moon is irregular, about 27 × 22 × 18 km. The 22.533 km comparison diameter is representative rather than a spherical edge.
The marked representative mean diameter is calibrated. Unmeasured illustration details are representative.
Use the visual comparison to explore its scale, then check the measurements and sources.
Change your perspective
Put it next to…
Choose a suggestion to redraw the comparison, or open its page to learn what it is.
Why this measurement?
Why we use 32 km
We compare the main-channel length of the Onyx River. This is an estimate; check the notes for its rounding and uncertainty. The recorded range is 28 km to 35 km.
Antarctica’s seasonal Onyx River is commonly described as approximately 32 km long. Its meltwater course, active reach and mapped endpoints vary with season and survey convention.
The marked horizontal span follows the measured feature, not the edges of the image. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 32 km | 28 km to 35 km | approximate |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valuePlanets, moons and spacePhobos22.53 kmRepresentative mean diameterPhobos is the larger and innermost moon of Mars, notable for its irregular shape and heavily cratered surface.Around the same scalePeople and human anatomyOne-hour cycle20 kmDistanceA one-hour cycle is the distance covered by cycling at a constant speed for one hour without stopping.
Nearest higher valuePlanets, moons and spaceMetis43 kmMean-equivalent diameterMetis is an irregularly shaped inner moon of Jupiter, orbiting close to the planet's cloud tops.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- US Antarctic Program — Onyx RiverMcMurdo Dry Valleys geographic context; published river length and active course are approximate.
There’s always another scale
Follow your curiosity.
PlacesRiver Thames346 kmThe River Thames is a major river in southern England that flows through London and empties into the North Sea.PlacesRoe River61 mThe Roe River is a short river in Montana, USA, flowing from Giant Springs to the Missouri River.SpacePhobos22.53 kmPhobos is the larger and innermost moon of Mars, notable for its irregular shape and heavily cratered surface.PeopleOne-hour cycle20 kmA one-hour cycle is the distance covered by cycling at a constant speed for one hour without stopping.
SpaceNeutron star20 kmA neutron star is the dense remnant core left after a massive star explodes as a supernova, composed mostly of neutrons.PlacesChallenger Deep10.94 kmChallenger Deep is the deepest known point in the Earth's oceans, located in the Mariana Trench.TransportOne-hour drive at 100 km/h100 kmA one-hour drive at a set speed is the distance a vehicle travels in one hour of uninterrupted motion.
SpaceDeimos12.4 kmDeimos is the smaller and outermost natural satellite of Mars, with an irregular, rocky shape.