Introduction This talk will focus on X-rays from bodies in the solar system… … starting with the Earth… … and ending with Saturn! (passing through Mercury [Moon], Venus, Mars, Asteroids and Jupiter on the way!) (and missing out the Sun and comets!)
Earth The Earth is not normally observed by X-ray instruments – but we did observe the Earth with D-CIXS on SMART-1 …... and were lucky enough to see it (twice!). Unfortunately, D-CIXS isn’t an imaging instrument but a spectral instrument …
D-CIXS – X-rays from the Earth! +45 o 0o0o -45 o
Red line is the smoothed D-CIXS light curve from the two Earth scans…
… and the green line is the (scaled) short wavelength X-ray light curve from the Sun!! [GOES-12 data] The near perfect agreement between the green and red light curves indicates conclusively that we are seeing solar induced X-ray fluorescence from the Earth’s atmosphere. Both double peaked! The difference in response here is due to the collimator – the Earth scan has already passed over the sunlit Earth, so the signal is only coming through the “side” of our response, rather than the peak for the first flare (by chance). D-CIXS – Earth Scans
Earth in D-CIXS Field-of-View At the time of the first flare, the Earth was about half in the D-CIXS field-of- view and covered the centre of the field … …while for the second flare, about 1/3 rd of the Earth had disappeared out the top of our field-of-view and the Earth didn’t cover the centre of the field.
Centre facet Large X1.5 solar flare on 16 th July, 2004. D-CIXS – Earth Scans
Earth Argon Glow Centre facet Total summed spectrum from centre facet ~2100 counts in the Argon peak! D - CIXS Observation X Flare level Large X1.5 solar flare on 16 th July, 2004.
Earth – X-ray Aurora! The Earth can also generate X-rays from the Sun in a different way … … if energetic particles from the Sun hit the Earth, the Earth’s magnetic field deflects them towards the magnetic poles and we see Aurora from the ground … … and X-ray aurora from space! From the ground (looking up!) Or from space (looking down!)
July 5 th – C3 Flare … … the largest flare seen by C1XS! Mercury (Moon!)
July 5 th – C3 Flare - C1XS spectrum (linear scale) Clearly highland terrain based on strong Al line! Clearly highland terrain based on strong Al line! Lines way stronger than normal detector background. Lines way stronger than normal detector background. C3 flare sufficiently strong to excite Ca! C3 flare sufficiently strong to excite Ca! But, if we go to a log scale, can we see anything else lurking in the undergrowth … But, if we go to a log scale, can we see anything X else lurking in the undergrowth … Mg Al Si
July 5 th – C3 Flare Ca K α Ca K β Fe K α Ti K α Cr K α? Mn K α? K K α? Solar Ar line ? Solar Fe line ? C1XS Av. Spec. Peak Spec.
Venus Venus was observed by Chandra on January 10 th and 13 th, 2001 – and detected! The emission was mainly in the lines of oxygen, carbon, and, marginally, nitrogen… Dennerl et al., A&A 2002 Chandra Observation!
Venus – Spectrum Spectra of Venus and the “background sky” show a clear detection of oxygen from Venus! The image and spectrum are consistent with the idea that this is also X-ray fluorescence – i.e. like the Moon and Mercury – only here it is from the atmosphere rather than the “hard” surface (like the Earth’s argon glow!).
Mars Mars was observed by Chandra on July 4 th, 2001! Mars was detected for the first time in X-rays… …the spectrum once again indicates that the emission is from oxygen … … and this is (once again!) consistent with solar fluorescence! However, “other” X-rays have been detected from Martian rocks … … although, admittedly, we had to take the “X-rays” there ourselves!
X-rays – from Martian rocks! The Alpha Particle X-ray Spectrometer (APXS) on the Spirit Mars rover looked at rocks and soils in Gusev Crater and Colombia Hills and measured the major and many minor elements. The rocks resemble volcanic rocks of primitive basaltic composition. However, bromine in certain rocks could indicate the presence of water in recent times … !!
Asteroid – 433 Eros NEAR-Shoemaker started orbiting 433 Eros on Feb. 14 th, 2000 and obtained lots of incredible images and a few X-ray spectra. The results show that Eros is a very primitive object. [NB: The *3* lines here are NOT resolved by the NEAR Si X-ray detector!]
Asteroid - Itokawa The Japanese mission “Hayabusa” was launched on May 9 th, 2003 to fly to the asteroid (25143) Itokawa. Itokawa is much smaller than Eros – just 600m across! Hayabusa attempted TWICE to soft-land (“touch down”) on Itokawa and retrieve a few grams of surface material before bounching off again. Indications are that the 2 (or 3?) attempts probably failed, but there could still be dust and stuff on Hayabusa. Hayabusa then FINALLY returned to Earth – landing in the Australian outback a few weeks ago!
Jupiter Jupiter possesses a very strong magnetic field – which tries to resist the flow of protons and electrons from the Sun – called the solar wind. This means particles from the Sun are deflected and can only reach Jupiter via the “cusps” at Jupiter’s magnetic poles … … in other words – particles from the Sun will land on Jupiter’s auroral region. Of course, X-rays from the Sun are not affected and can land anywhere on Jupiter …
Jupiter – X-rays This X-ray image of Jupiter from Chandra (left) clearly shows a concentration of X- rays from the poles of Jupiter … … this immediately suggests particles (electrons?) are involved … … there is also a fainter glow from the whole planet which is the normal X-ray fluorescence we have already seen from all the other solar system objects so far. Jupiter’s aurora is also visible in this HST image …
SURPRISING : Northern auroral X-rays are localized in latitude (60-70 o ) and longitude (160- 180 o ) Concentrated in a “HOT SPOT” The X-ray hot spot is located poleward (higher magnetic latitude) than the main ultraviolet auroral oval: obtained from simultaneous HST-STIS observations Polar projections of X-rays seen by Chandra and simultaneous far- ultraviolet (FUV) images obtained by the Hubble Space Telescope. Jupiter – X-rays
But that is not the whole story! When you look at the timing of the X-ray emission … … it is obvious that the X-rays are pulsed in some way!?
PUZZULING : The X-ray hot spot mysteriously pulsates with a period of ~42 minutes Movie of x-ray HOT SPOT Light-curve and power-spectrum data for the auroral hot spot. Jupiter – X-ray Timing
Chandra ACIS Images of Io and Europa (250 eV < E < 2 keV) Nov.25-26, 1999 The axes are labeled in arcsec. 1 arcsec 2295 km Chandra HRC- I Image of Io Dec. 18, 2000 Scale bar - smoothed counts per image pixel (0.492 by 0.492 arcsec) R Io = 1820 km R Europa = 1560 km [R Moon = 1738 km] Discovery of X-rays from Galilean Satellites of Jupiter
Saturn After Jupiter – the detection of Saturn was the next target! Of course, Saturn is further away from Earth (and the Sun!) … … nearly twice as far away as Jupiter (so even if it was the same X-ray brightness as Jupiter – it would appear 4 times fainter… ) Saturn certainly has aurora – like Jupiter! So, it was no surprise when Chandra took this image … right? … well, actually, there is a bit of a problem here!
Saturn Jupiter ? Saturn’s X-rays clear don’t come from the poles like Jupiter … … and the X-ray spectrum clearly looks like the Sun … … so it is X-ray scattering from Saturn’s cloud tops … … only, the flux is about 50 times stronger than expected!? It is therefore surprising that we DON’T see Saturn’s rings in X-rays … !?
From our understanding of X-rays observed from Planets and Moons: We expect X-rays from: 1.Titan [dense atmosphere – like Earth (N 2 )] 2.Inner satellites of Saturn [analogy to Jovian Moons] 3.Uranus and Neptune [natural expectation !] We wait optimistically !!! Future … Of course, they will be much fainter than Jupiter and Saturn and Jupiter’s Moons...
Earth (auroral) Jupiter (auroral) Galilean satellites (Io, Europa, Ganymede) Io Plasma Torus Magnetosphere Solar X-rays (Corona) Solar Wind (Coronal Holes) Sun Mercury (Moon, asteroids) Venus Earth (Non-auroral) Jupiter (Non-auroral) Comets Jupiter (auroral) ?? Basic Energy Source(s) of X-ray Emission from Solar System Objects
Conclusions If you have been keeping track of the observations I have been showing you, you will have noticed that the earliest one was dated 2000 (one was Nov. ’99 actually – but ALL the rest where 2000 and onwards!)! Indeed, if I had given this talk prior to about 1991 – it would have just consisted of the Sun and the Earth! Things have moved on considerably in the last few years and we are just entering a “golden age” of planetary X-ray science.
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