The Sun
Position on the route: 21/45 · level needed 45 · journey (Mk0 engine) 17.0 h
By the numbers
| Diameter | 1,392,700 km (109 Earths) |
|---|---|
| Mass | 99.86 % of the system |
| Surface | ≈ 5,500 °C |
| Core | ≈ 15 million °C |
| Light takes | 8 min 20 s |
| Age | 4.6 billion years |
The story
The Sun is a G-type main-sequence star carrying 99.86 % of the Solar System’s mass: 73 % hydrogen, 25 % helium. In its core about 600 million tonnes of hydrogen fuse into helium every second; the energy spends tens of thousands of years working its way out as photons, then crosses to Earth in eight minutes.
Above the surface (photosphere) lie the chromosphere and a corona millions of degrees hot. Sunspots, flares and coronal mass ejections rise and fall in an 11-year cycle; on Earth they give aurorae and now and then break satellites and power grids. In about 5 billion years the Sun will swell into a red giant.
Sending humans to the Sun is impossible, but probes go. To ‘fall’ into the Sun a probe must cancel almost all of Earth’s orbital speed (30 km/s), which takes more fuel than a trip to Pluto. That is why probes like Parker use Venus’s gravity again and again to creep closer.
Missions
- SOHO (ESA/NASA, 1995): continuous observation
- SDO (NASA, 2010): an image every 12 seconds
- Parker Solar Probe (NASA, 2018–): the first craft into the corona, 6.1 million km in 2024
- Solar Orbiter (ESA, 2020–): the first polar images
Colony note
It cannot be colonised. Only ‘solar probes’ with a special heat shield can approach; each flight brings back some of the most expensive and most valuable data in science.
What probes bring back
- Parker Solar Probe entered the corona in 2021: the first time a spacecraft has passed through a star’s atmosphere. In 2024 it swept past at just 6.1 million km from the surface at 690,000 km/h.
- The corona is 1–3 million degrees while the surface is only 5,500 °C: the ‘coronal heating problem’, one of solar physics’s biggest open questions. Magnetic reconnection and Alfvén waves are the suspects.
- The fast solar wind streams out of coronal holes; Parker found ‘switchbacks’, folds of reversing magnetic field in the slow wind.
- The 11-year solar cycle: sunspots and storms rise and fall. The 1859 Carrington event set telegraph lines on fire; the same today could hit power grids and satellites.
- Solar Orbiter (2020) is imaging the Sun’s poles up close for the first time; SOHO (1995) has spotted more than 4,000 comets.