30 Years in Space: The Voyagers

and the Distant Heliosphere

Péter KirályKFKI Research Institute for Particle and nuclear Physics,

Budapest, Hungary

Kosice, 06 June 2007.

The „hairy Sun”

Model magnetic field in the solar corona.

Solar wind (SW) and energetic particles have to find their

way out of the tangle of field lines.

Old picture of planetary orbits and of the heliospheric boundary region, with Pioneers still alive

Ian Axford’s early model and how it looks in my kitchen sink

Our galactic environment on a logarithmic scale

The interstellar environment of our Heliosphere

The Voyagers and the boundary regions

of the Heliosphere

Some important dates

1972 - 73: launch of Pioneer 10 and 11

1977 Aug. - Sept.: launch of Voyager 1 and 2

1989: Last planetary encounter of V2 (Neptune)

2002 May: First pre-shock flux enhamcements at V1

2004 Dec.: Termination shock (TS) crossing of V1

2005 May: First pre-shock flux enhamcements at V2

2007 …. : Termination shock (TS) crossing of V2?

The two Voyager space probes, launched in 1977, have now crossed (V1) or approached (V2) the boundary of the supersonic solar wind “bubble”.

Up-to-date sketch of the heliospheric interface with the

interstellar wind

(V. Izmodenov et al., A&A 429, 1069–1080, (2005)

The terrestrial magnetosphere (from the Oulu Space Physics Textbook)The Heliosphere is about 100 000 times bigger, and has a SW bubble.

Voyager 1, 2 radial and angular positions, and their separation

The Low Energy Charged Particle Detector (LECP) aboard both Voyagers.

A rotating platform turns the particle detectors into 7 directions (and back), and measures particle flux in each direction. Thus both energy spectra and directional distributions are continuously monitored.

The platform has faultlessly worked on both Voyagers for almost 30 years!

Look directions for low-energy V-1 and V-2 rotating platform

detectors (V-2 was flipped in 1992, new guide star chosen)

V-1 V-2

In December 2004 Voyager-1 crossed the heliospheric termination shock

In mid-August 2006 Voyager-1 passed the 100 AU distance mark.

The solar distance of Voyager-2 exceeded 80 AU in July 2006.

V-2 is still in the supersonic solar wind, while V-1 is exploring the subsonic Heliosheath since mid-December 2004.

This Summer both Voyagers will celebrate their 30-year anniversary.

The termination shock crossing of Voyager-2 may occur any time now.

Just as the Sun is the most accessible star, our Heliosphere is the most accessible astrosphere. The termination shock separating supersonic and subsonic SW is expected to be an acceleration site, and in situ data from that region may have implications on our understanding of cosmic shocks.

Low-energy ion count rates and their day-to-day variability

Two years ago:

Time histories:

> 0.5 MeV ion count logarithmic rates (top),

day-to-day flux variability (middle), (i.e. absolute values of log ratios for subsequent days)

spectral slopes derived from 40 keV to 4 MeV LECP ion channels, without BG correction (bottom).

Characteristic changes of omnidirectional energetic particle rates for V-1

V1 omnidirectional low-energy count rate

and a logarithmic measure of its day-to-day variability

How TS-related energetic particle activity started in 2002 at Voyager 1 and in 2005 at Voyager 2

(from Horst Fichtner’s ICRC rapporteur paper in Tsukuba, 2005)

V-2: How low-energy ion count rate and its variabilty

increased throughout the last two years

The most recent low-energy Voyager-2 results (up to 2nd June 2007)

Simultaneous Voyager-2 energetic proton flux and SW variations from start of flux increases to mid-2006 (taken from online LECP team plot).

The effects of a huge SW shock at late February 2006 are clearly seen.

That shock may temporarily have pushed out the TS by several AU, and delayed progress towards solar minimum modulation of CRs above 70 MeV by about half a year.

V-2 energetic proton data and SW parameters as before, but

up to April 2007.

„CR” count rates above 70 MeV

5-year histories of the Cosmic Ray Subsystem (CRS) high-energy count rates as detected by both Voyagers

V-2

V-1 (delayed by 110 days)

>70 Mev „CR” rates, V-1 shifted left by 110 days (favoured)

Recent variations of the SW speed at V-2

LECP omnidirectional ion fluxesin narrow energy bins

V-1 LECP fluxes up to late April (on linear scale, without BG correction)

V-2 LECP fluxes up to late April (on linear scale, without BG correction)

Directional distributions,

streaming directions

(Time histories of smoothed amplitudes and phases of first-order

anisotropies)

Amplitudes and phases of 1st harmonics of lower-energy V-1 LECP directional fluxes (10 and 30-day smoothing, resp., no BG correction).

Amplitudes and phases of 1st harmonics of higher-energy V-1 LECP directional fluxes (10 and 30-day smoothing, resp., no BG correction).

Amplitudes and phases of 1st harmonics of lower-energy V-2 LECP directional fluxes (10 and 30-day smoothing, resp., no BG correction).

Amplitudes and phases of 1st harmonics of higher-energy V-2 LECP directional fluxes (10 and 30-day smoothing, resp., no BG correction).

2 to ~4 MeV fluxes for V-1 and V-2 (top), 1st harmonic amplitudes and phases for V-1 (middle) and for V-2 (bottom)

Conclusions• Voyager-1 crossed the termination shock (that was moving inward) in

mid-December 2004.

• The shock spike was seen mainly at suprathermal energies.

• Anisotropy substantially decreased downstream of the shock..

• Voyager-2 also detects increased intermittent fluxes (since May 2005).

• While V-1 mainly saw outward streaming along the spiral field before shock-crossing, the streaming at V-2 is mainly inward along the spiral.

• Voyager-2 may cross the termination shock soon.

• Solar wind speed has not changed at Voyager-2 so far. At shock crossing dramatic decreases are expected.

Extra

Temperatures of the solar corona inferred from the ionization state of ions measured by Ulysses

Effects of a simple-minded background subtraction on

amplitudes and phases of the lowest-energy V-1 LECP data (BG corrected plot on top).

Effects of a simple-minded background subtraction on

amplitudes and phases of the lowest-energy V-2 LECP data (BG corrected plot on top).

The recent dynamic pressure at V-2 (reduced to 1 AU)

was comparable to the largest earlier ones