Has SOHO ended a 30-year quest for solar ripples?

May 03, 2007

The ESA-NASA Solar and Heliospheric Observatory (SOHO) may have glimpsed long-sought oscillations on the Sun's surface. The data will reveal details about the very core of our central star and it contains clues as to how the Sun formed, 4.6 billion years ago.

The subtle variations reveal themselves as a minuscule ripple in the overall movement of the solar surface. Astronomers have been searching for ripples of this kind since the 1970s, when they first detected that the solar surface was oscillating in and out.

The so-called 'g-modes' are driven by gravity and provide information about the deep interior of the Sun. They are thought to occur when gas churning below the solar surface plunges even deeper into our star and collides with denser material, sending ripples propagating through the Sun's interior and up to the surface. It is the equivalent of dropping a stone in a pond.

Unfortunately for observers, these waves are badly degraded during their passage to the solar surface. By the time g-modes reach the exterior, they are little more than ripples a few metres high. To make matters more difficult, the g-modes take between two and seven hours to oscillate just once. So, astronomers are faced with having to detect a swell on the surface that rises a metre or two over several hours.

Now, however, astronomers using the Global Oscillation at Low Frequency (GOLF) instrument on SOHO think they may have caught glimpses of this behaviour. Instead of looking for an individual oscillation, they looked for the signature of the cumulative effect of a large number of these oscillations.

By analogy, imagine that the Sun was an enormous piano playing all the notes simultaneously. Instead of looking for a particular note (middle C for instance) it would be easier to search for all the 'C's, from all the octaves together.

In the piano their frequencies are related to each other just as on the Sun, one class of g modes are separated by about 24 minutes.

"So that's what we looked for, the cumulative effect of several g modes," says Rafael A. García, DSM/DAPNIA/Service d'Astrophysique, France. They combined ten years of data from GOLF and then searched for any hint of the signal at 24 minutes. They found it.

"We must be cautious but if this detection is confirmed, it will open a brand new way to study the Sun's core," says García.

Until now, the rotation rate of the solar core was uncertain. If the GOLF detection is confirmed, it will show that the solar core is definitely rotating faster than the surface.

The rotation speed of the solar core is an important constraint for investigating how the entire Solar System formed, because it represents the hub of rotation for the interstellar cloud that eventually formed the Sun and all the bodies around it. The next step for the team is to refine the data to increase their confidence in the detection. To do this, they plan to incorporate data from other instruments, both on SOHO and at ground-based observatories.

"By combining data from space (VIRGO and MDI, on SOHO) and ground (GONG and BiSON) instruments, we hope to improve this detection and open up a new branch of solar science," says García.

Source: European Space Agency

Explore further: Far from home: Wayward cluster is both tiny and distant

add to favorites email to friend print save as pdf

Related Stories

OSIRIS catches glimpse of Rosetta's shadow

21 hours ago

Several days after Rosetta's close flyby of comet 67P/Churyumov-Gerasimenko on 14 February 2015, images taken on this day by OSIRIS, the scientific imaging system on board, have now been downlinked to Earth. ...

Seafloor holds 15 million years of monsoon history

Mar 02, 2015

When the research vessel JOIDES Resolution returned to port in late January after a two-month cruise, it had harvested more than 550 sediment cores from deep beneath the Indian Ocean. Locked within those ...

NASA spacecraft nears historic dwarf planet arrival

Mar 02, 2015

NASA's Dawn spacecraft has returned new images captured on approach to its historic orbit insertion at the dwarf planet Ceres. Dawn will be the first mission to successfully visit a dwarf planet when it enters ...

What is Mars made of?

Feb 26, 2015

For thousands of years, human beings have stared up at the sky and wondered about the Red Planet. Easily seen from Earth with the naked eye, ancient astronomers have charted its course across the heavens ...

A recipe for returning Pluto to full planethood

Feb 20, 2015

A storm is brewing, a battle of words and a war of the worlds. The Earth is not at risk. It is mostly a civil dispute, but it has the potential to influence the path of careers. In 2014, a Harvard led debate ...

Recommended for you

Planet 'reared' by four parent stars

3 hours ago

Growing up as a planet with more than one parent star has its challenges. Though the planets in our solar system circle just one star—our sun—other more distant planets, called exoplanets, can be reared ...

Far from home: Wayward cluster is both tiny and distant

Mar 03, 2015

Like the lost little puppy that wanders too far from home, astronomers have found an unusually small and distant group of stars that seems oddly out of place. The cluster, made of only a handful of stars, ...

An old-looking galaxy in a young universe

Mar 02, 2015

A team of astronomers, led by Darach Watson, from the University of Copenhagen used the Very Large Telescope's X-shooter instrument along with the Atacama Large Millimeter/submillimeter Array (ALMA) to observe ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.