© 2010 RAL Space

X-rays From The Solar System

Barry J. Kellett

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!

+45o

0o

-45o

D-CIXS – Earth Scans

D-CIXS – Earth Scans

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

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 1/3rd 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 16Large X1.5 solar flare on 16 thth July, 2004. 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 16th July, 2004.

Earth – X-ray Aurora!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 5July 5thth – C3 Flare … – C3 Flare …

… … the largest flare seen by the largest flare seen by C1XS!C1XS!

Mercury (Moon!)

•

July 5July 5thth – C3 Flare - C1XS spectrum (linear – C3 Flare - C1XS spectrum (linear scale)scale)

• Clearly highland terrain based on strong Al Clearly highland terrain based on strong Al line!line!

• Lines way stronger than normal detector Lines way stronger than normal detector background.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 But, if we go to a log scale, can we see anything anything X else lurking in the else lurking in the undergrowth …undergrowth …

Mg

Al

Si

• July 5July 5thth – C3 Flare – C3 Flare

Ca KCa Kαα

Ca Ca KKββ

Fe KFe KααTi KTi KααCr KCr Kαα??

Mn Mn KKαα??

K K KKαα??

Solar Solar Ar Ar lineline?? Solar Solar

Fe Fe lineline??

C1XS C1XS Av. Spec.Av. Spec. Peak Peak Spec.Spec.

Venus• Venus was observed by Chandra on January 10th

and 13th, 2001 – and detected!• The emission was mainly in the lines of oxygen, carbon,

and, marginally, nitrogen…

Dennerl et al., A&A 2002

Chandra Observation!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 4th, 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. 14th, 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 9th, 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 (60-70o) and longitude (160-180o) Concentrated in a “HOT SPOT”

The X-ray hot spot is located The X-ray hot spot is located poleward (higher magnetic poleward (higher magnetic latitude) than the main latitude) than the main ultraviolet auroral oval: ultraviolet auroral oval: obtained from simultaneous obtained from simultaneous HST-STIS observationsHST-STIS observations

Polar projections of X-rays seen by Chandra and simultaneous far-ultraviolet (FUV) images obtained by the Hubble Space Telescope.

Jupiter – X-raysJupiter – X-rays

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 :PUZZULING : The X-ray hot The X-ray hot spot spot mysteriously pulsates mysteriously pulsates with a period of ~42 minuteswith 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 TimingJupiter – 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 IoDec. 18, 2000

Scale bar - smoothed counts per image pixel (0.492 by 0.492 arcsec)RIo = 1820 km

REuropa = 1560 km[RMoon = 1738 km]

Discovery of X-rays from Galilean Discovery of X-rays from Galilean Satellites of JupiterSatellites 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 From our understanding of X-rays observed from Planets and Moons:Planets and Moons: We expect X-rays from:We expect X-rays from:

1. Titan [dense atmosphere – like Earth (N2)]

2. Inner satellites of Saturn [analogy to Jovian Moons]

3. Uranus and Neptune [natural expectation !]

We wait optimistically !!!

Future … 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 Basic Energy Source(s) of X-ray Emission from Solar System ObjectsSolar 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.

© 2010 RAL Space

© 2010 RAL Space