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

May 3, 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: Mercury found to be tectonically active

Related Stories

Mercury found to be tectonically active

September 26, 2016

Images acquired by NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show geologic features that indicate Mercury is likely still contracting today, joining Earth as a tectonically ...

Earth's carbon points to planetary smashup

September 5, 2016

Research by Rice University Earth scientists suggests that virtually all of Earth's life-giving carbon could have come from a collision about 4.4 billion years ago between Earth and an embryonic planet similar to Mercury.

What is the temperature of the Earth's crust?

September 19, 2016

As you may recall learning in geology class, the Earth is made up of distinct layers. The further one goes towards the center of the planet, the more intense the heat and pressure becomes. Luckily, for those of us living ...

Ceres: The tiny world where volcanoes erupt ice

September 1, 2016

Ahuna Mons is a volcano that rises 13,000 feet high and spreads 11 miles wide at its base. This would be impressive for a volcano on Earth. But Ahuna Mons stands on Ceres, a dwarf planet less than 600 miles wide that orbits ...

Recommended for you

Scientists investigate unidentified radio sources

September 28, 2016

(Phys.org)—A team of researchers led by Andrea Maselli of the Institute of Space Astrophysics and Cosmic Physics of Palermo, Italy, has conducted an observational campaign of a group of unassociated radio sources with NASA's ...

Research resolves a debate over 'killer electrons' in space

September 28, 2016

New findings by a UCLA-led international team of researchers answer a fundamental question about our space environment and will help scientists develop methods to protect valuable telecommunication and navigation satellites. ...

Kepler watched a Cepheid star boil

September 28, 2016

After four years of continuous monitoring, astronomers detected clear signs of convective cells in a giant pulsating star for the first time using the Kepler space telescope.

The ultraviolet diversity of supernovae

September 28, 2016

Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside their progenitor stars, including ...

0 comments

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.