Spaceprobes in the Solar System

The diagram above (click to zoom) and list below show currently active spacecraft in the Solar System, not including those operating close to the Earth (and I’ve probably missed a few):

  • Voyager 1 and Voyager 2, launched in 1977, now heading into the darkness and still reporting back, even though they are over 17 billion km or 16 light-hours away (not shown above).
  • Cassini–Huygens, launched in 1997, now in the final stages of its exploration of Saturn (see fact sheet).
  • 2001 Mars Odyssey, launched in 2001, and still orbiting Mars.
  • New Horizons, launched in 2006, now en route from Pluto to the Kuiper belt object 2014 MU69, which it should reach in January 2019.
  • Dawn, launched in 2007, currently orbiting Ceres (image shown above the Earth).
  • Akatsuki, launched in 2010, currently orbiting Venus, which it will do until 2018.
  • Juno, launched in 2011, currently orbiting Jupiter, which it will do until February 2018.
  • Hayabusa 2, launched in 2014, currently en route to asteroid 162173 Ryugu, which it should reach in 2018. It will then take a sample which should arrive back home in 2020 (not shown above).
  • ExoMars Trace Gas Orbiter, launched in 2016, currently orbiting Mars and mapping the Martian atmosphere (the associated Mars lander was lost in 2016).
  • OSIRIS-REx, launched in 2016, currently en route to asteroid 101955 Bennu, which it should reach in 2018. It will then take a sample which should arrive back home in 2023 (image shown below the Earth).

In addition to the above, BepiColombo is scheduled to launch for Mercury in October 2018, and SolO is scheduled to launch for the Sun that same month. Also, InSight is scheduled to launch for Mars in May 2018, and Solar Probe Plus is scheduled to launch for the Sun in August 2018.

Metallic hydrogen

It has long been known that hydrogen forms a metallic solid at moderate to low temperatures and extremely high pressures. Last year, Ranga Dias and Isaac F. Silvera at Harvard University were the first to actually produce this metal, using the enormous pressure of 495 gigapascals (see their paper).

At higher temperatures, hydrogen forms a metallic liquid, and this is believed to exist at the heart of Jupiter and Saturn. This liquid has yet to be observed.

The ExoMars lander

The ESA/RFSA ExoMars lander seems to have crashed on Mars, unfortunately. The chart above shows the planned sequence of events (which was to have ended with a soft collision). Instead, we seem to have had an early parachute release, with a very brief use of thrusters, followed by loss of signal after 19 seconds – consistent with free-fall to the surface under Martian gravity.

Update: the crash site seems to have been identified.

A scale model of the Solar System

The following images of the eight major planets and Pluto are to scale, with each image 500,000 km in width (the third image also includes the Moon). For comparison, the diameter of the Sun is 1,390,000 km, so you can team these planets up with a yellow circle 2.8 times the width of each image. Click on the images (which can also be found on the Homeschool Resources section of this blog) to zoom.


If you want distances from the Sun to each planet to be to scale as well (like this or this), they are shown below (in millions of km and multiples of the width of each image). If the images above are printed out 5 cm or 2 inches wide (i.e. at a scale of 1 cm = 100,000 km), then the sun would be 14 cm (5.5 inches) wide, and distances from the Sun to each planet would be as per the bottom two rows of the table.

58 108 150 228 779 1,434 2,872 4,495 5,906 million km
120 220 300 460 1,560 2,870 5,700 9,000 11,800 multiples
6 11 15 23 78 140 290 450 590 metres
19 35 49 75 260 470 940 1470 1940 feet

The image below (click to zoom) shows the complete solar system, but most planets are too small to see:

Juno arrives!

The Juno spaceprobe (above) is just an hour away from orbit insertion around Jupiter. Juno has been in transit, waiting for this day, for almost five years. Juno is solar-powered, with huge 9-metre-long solar panels, to compensate for the fact that the intensity of sunlight around Jupiter is only 4% of what it is here.

Follow the spaceprobe on Twitter or watch the live NASA feed (which is starting now).

Update 1: Juno is into its orbit insertion burn, screaming past Jupiter at a distance of 5,000 km and a velocity of 208,000 km/hr.
Update 2: Engine off. “Juno, welcome to Jupiter!” (NASA/JPL clapping)

Arriving at Jupiter

The Juno spaceprobe (above) is a few days from reaching Jupiter, and beginning its mission of studying that giant planet. Juno has been in transit for almost five years, as shown below:

Juno is now just under 4 million kilometres away from Jupiter. She will spend more than a year examining Jupiter in detail, and will then deorbit, carrying a plaque in honour of Galileo, who discovered that there were moons orbiting that planet.

As seems to be the norm nowadays, the spaceprobe has a Twitter feed for staying in touch. There will certainly be some interesting stories and pictures to come!