Abstract
Captain Kirk stands at his console. He’s in trouble again, and needs to consult with Star Fleet Command back on Earth. Despite the fact that the Enterprise is 20,000 light-years from Earth, Kirk is able to talk, in real time, to his superiors, which ultimately enables him to save the universe. Kirk is able to ignore the great distances in the galaxy by the use of subspace radio, a clever invention engineered by…Hollywood. But the truth is that we have no such technology, and when we communicate with our spacecraft emissaries throughout the Solar System, their distances are underlined by the long time lag in our transmissions to and from them. When a spacecraft – for example, Voyager 2 – is out at Neptune, still well inside our cosmic backyard by Captain Kirk’s standards, one-way communication takes just under 4 h. That is, the time it takes light (or radio waves) to travel from Earth to Neptune at its closest point in its orbit is roughly 3 h and 54 min. It is a very long way to Neptune.
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Notes
- 1.
When Voyager encountered Neptune, the two planets happened to be near each other in their orbital trek, both on the same side of the Sun. Had Neptune been opposite the Earth, Voyager’s 246 min light-time would have stretched to some 8 h.
- 2.
Or even hours, depending on the timing of orbiting relay stations such as the Mars Reconnaissance Orbiter or ESA’s Mars Express.
- 3.
Even sending a radio message to our own Moon next door takes effort. At a distance of 240,000 miles away, radio signals take 1½ s to travel the one-way distance.
- 4.
In terms of travel time, but not necessarily distance.
- 5.
Earlier, Plato had estimated Earth’s diameter at 2250 km.
- 6.
Mars may have had something similar to plate tectonics at one time. Magnetic patterns in Martian rock seem to contain repeating patterns similar to those on Earth’s ocean floors where the seafloor has spread apart. If so, this process ended long ago. Jupiter’s moon Europa also appears to have had similar movements across regions of its ice crust, but these motions are related more closely to sea ice drift.
- 7.
Liquid water may also play an important role.
- 8.
The Yellow River is the 6th longest river in the world, but Baltis Valles could easily have rivaled our longest, the Nile (6650 km).
- 9.
1321 Earths would fit inside Jupiter, 764 for Saturn, 63 for Uranus and 57 for Neptune.
- 10.
In fact, pressures become so great that raining carbon particles may transform into house-sized diamonds deep within these colossal worlds.
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© 2016 Springer International Publishing Switzerland
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Carroll, M. (2016). A Tour of the Planets. In: Picture This!. Springer, Cham. https://doi.org/10.1007/978-3-319-24907-0_4
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DOI: https://doi.org/10.1007/978-3-319-24907-0_4
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