A recent study offers a possible explanation as to why Neptune’s system of satellites differs from those of other gas giants; it also indicates that Neptune’s proximity to the Kuiper Belt is what is responsible. At one time, Neptune may have had a system of moons that were very much like those of Jupiter, Saturn, and Uranus. But since it is well-situated to pick up dwarf planet-sized objects that were kicked out of the Kuiper Belt.
Above – Artist representation of the moon Triton.
The limit on our observation universe is not the age of the universe and the speed of light which would be 13.799 billion light-years for two reasons.
1. Space itself is expanding, so we can actually detect light from objects that were once close, but are now up to around 45.7 billion light years away (rather than up to 13.799 billion light years away as might be expected).
2. before the recombination epoch, about 378,000 years after the Big Bang, the Universe was filled with a plasma that was opaque to light, and photons were quickly re-absorbed by other particles, so we cannot see objects from before that time using light or any other electromagnetic radiation. Gravitational waves and neutrino background would have been unaffected by this, and may be detectable from earlier times.
The Lubin UCSB laser propulsion system efforts have been funded by Breakthrough Starshot for $100 million. They are working working to demonstrate proof of concept for light-propelled nanocrafts.
A large scale network of several 70 Gigawatt lasers on Earth, Earth Orbits, the moon Mars and asteroids is not as distant as one might think because of several converging systems and technological shortcuts.
A laser power of 70GW (without photon recycling) can send a 100 kg craft can be propelled to 1AU in approximately 3 days achieving a speed of 0.4% the speed of light, and a 10,000 kg craft in approximately 30 days.
The full scale DE-STAR 4 (50-70 GW) will propel a wafer scale spacecraft with a 1 meter laser sail to about 26% the speed of light in about 10 minutes (20 kgo accel), reach Mars (1 AU) in 30 minutes, pass Voyager I in less than 3 days, pass 1,000 AU in 12 days and reach Alpha Centauri in about 20 years. The same directed energy driver (DE-STAR 4) can also propel a 100 kg payload to about 2% c and a 10,000 kg payload to more than 1,000 km/s. While such missions would be truly remarkable, the system is scalable to any level of power and array size where the tradeoff is between the desired mass and speed of the spacecraft.
A powerful 70 gigawatt laser propulsion system that could accelerate an 100 kilogram object over 122 seconds to 2% of light speed (6000 kilometers per second) would also be able to fire kinetic projectiles at nuclear weapon power.
The goal of the Breakthrough Starshot program (which has $100 million in funding) is to send wafer chip spacecraft to 20% of lightspeed to probe exoplanets and other star systems. The initial $100 million would not reach that goal but a follow on program for a few tens of billions of dollar could achieve it.
A 100 kilogram object accelerated to 2% of light speed (6000 kilometers per second) would have a kinetic impact of 430 kilotons of TNT.